Why are measure words omitted after specifiers and before some verbs?

Question

这（个）是我的，this is mine: Before 是，normally I would omit 个 这没有道理, this doesn't make sense: Before 有 I would find 个 strange. Although maybe that is because 有道理 is an abstract concept. If I was talking about which car has gas, I would say 这辆有汽油, not omitting the measure word. 这个在我房间里：This one is in my room: I would find it strange to omit 这 before 在.

So what's going on here? I have an intuitive sense (which I think is correct, but maybe it's not) about when the measure word can or should be omitted after specifiers. But I can't find a unifying theory that explains it.

Answer 1

As long as the measure word is not the focus of the sentence, it can always be omitted after a specifier (这／那). This is true regardless of the verb that comes afterwards.

The measure word cannot be omitted for multiple items/things with "quantity" carries weight for clarity that can't be replaced by a gesture or an arrangement.

For instance,

这兩个是我的 = 这是我的 - 兩个 can be omitted because you can simply point to the two items or the pile that contains two of them. However, in the sentence below:

这有兩个是我的. The sentence is incorrect with 兩个 omitted (这有是我的), nor 这是我的, as the original sentence is not item specific, and meant "any two" among many, the latter is very specific about the items, similar to saying "these two" out of many, or be twisted as claiming for "all".

这个没有道理 = 这没有道理. We understand this is pointing to a single event/thing, but consider:

这兩个假設没有道理. It is obvious that 兩个 carries weight for clarity, thus can't be omitted.

这辆(車)有汽油 = 这車有汽油 - the measure word 辆 can be omitted here. Also,

这个在我房间里 - 这在我房间里 - the measure word 个 can be omitted without causing confusion.

Answer 2

Compare to these:

这 -> this

这个 -> this one

So,

这是我的 -> this is mine.

这个是我的 -> this one is mine.