There is no "why". "是" in Chinese does not equal "be" in English. This is just how languages work.
In Chinese, almost anything can follow "是". The part after "是" is just a description or explanation of the part before "是", not an equivalent.
As a native Mandarin speaker this same question has puzzled me equally. I must emphasize that I don't claim to know more than the teachers, linguistics, and other smart people specializing in Mandarin. I can offer you a personal opinion based on my experiences. I can confirm iBug's answer that some sentence structures are omitted in oral and written speech. ...
Actually in your case, 是 means exactly "to be" in English.
However, it's important to realize in Chinese there are many ways to omit parts of speech, for example in Betty's sentences:
This one should be interpreted as:
Their return dates are set. Zhang's is tomorrow, and Li's is the day after ...
I think this 是 might be an example of 'illogical' sentences of the copula verb 是 (as described in Charles N. Li, Sandra A. Thompson, Mandarin Chinese: A Functional Reference Grammar), where 是 still means the verb to be but with a metaphorical meaning understood from the context. See for example these other answers:
Syntactic role of “我” in “我真是这个意思”
What is ...
So I am a native Chinese speaker and have never academically learned Chinese.
In short, "我是长头发" is not expected to appear in formal occasions or will be considered faulty, but in daily life we do use such experssion, only in oral Chinese, not written.
Nevertheless, "我是长头发" sounds weird to me. We use "我是个长头发（的人）" more often when ...
The only difference I can see is that "我的爸爸" is singular, while "公司的人" is plural.
That is the reason.
[V 的 V] = [the one who v, does v] e.g. "敵兵逃的逃，降的降" = "the enemy soldiers who run, do run; the enemy soldiers who surrender, do surrender". Which means 'some soldiers run, some soldiers surrender'.
打字的打字，打电话的打电话 = the ...
As a native speaker, I think 我是长头发 isn't grammatically correct. People may use it in oral speech, but it's still incorrect grammar. I never say/write anything like this. You are not a piece of hair but a human/man/woman/kid/student/worker etc.
I think a lot of native speakers make similar mistake like this (using something that are not supposed to describe a ...
远方 is more literary/ classical
遥远的地方 is more colloquial/ modern
我住在一个遥远的地方。= 'I live in a faraway place'
我住在远方。= 'I live in some faraway place'. We don't need the classifier 一个 for 远方, it is a term for 'far away place(s)' in general.
'我是长头发' should be interpreted as 'I am long-haired'.
In chinese we omit hyphen and suffixes like '-ed', '-ing', etc. You should modulate sentence until it makes sense.
I dont think chinese confuse '有' with '是', nor they mean 'my hair' by saying 'I'. They just have nouns and adjectives and verbs in the same form.
You don't really ask how old something is.
You're buying a second- hand microwave oven:
You're buying something you can use to do something:
You're buying a second-hand garment:
You're getting a second-hand boyfriend:
Is "它多大了?" Correct?
No, 多大 does not apply to objects only for human or animals
Depend on the type of article:
For something that is constantly in use
這電腦用了多少年了/ 多久了? (how long has this computer been in use)
這電視用了多少年了/ 多久了? (how long has this T.V. been in use)
For something last very long and rarely break down:
這自動手錶有多久歷史了? (How long is the history ...
You are trying to translate "我是长头发" in a way with correct grammar, but this Chinese sentence is used to describe a meaning, not a grammar structure. If we understand it following a strict grammar(literally) way, that sentence meas "I am long hair" which makes no sense.
The most important info in that sentence are "我" me and &...
I think "是" in this sentence "我是长头发" still means "be", and there is an ellipsis of "的人" at the end of the sentence.
我是长头发 -> 我是长头发[的人] I am [a person who has] long hair. -> I have long hair.
我是短头发 -> 我是短头发[的人] I am [a person who has] short hair. -> I have short hair.
我是卷头发 -> 我是卷头发[的人] I am [a person ...
This sentence itself means "I am the guy with long hair". And could vary on some dialogue context where some parts is omitted.
This sentence 我是长头发 is not common in Chinese, unless long hair is your distinctive feature, which is so distinct that it is like a nickname of you. No one is using this kind of sentence to describe a common feature without ...
As a Chinese native speaker, in daily life,
I prefer this understanding(not literally):
我是长头发。equal to 我(的头发)是长头发。My hair is long hair.
Moreover, any feature of mine after我是 I am means I have it., thus I can say 我是大眼睛。 I have big eyes.
也许 and 或许 are slightly subjective. They sometimes imply the intention of the speaker of believing in the suggested outcome or explanation.
也许他不是故意的。Maybe it wasn't on purpose.
The above may imply the speaker's intention of believing that It wasn't on purpose.
A similar word, 一般, implying a stronger intention, can sometimes be substituted.
要 usually means "want", but there are a few possible definitions to 想, 想 may possibly mean "think", or another possible definition is "want".
When compared, 要 has more confidence in tone compared to 想.