Our teacher of Chinese language and culture said this word means 因为. I stop my cart because of the evening scene of maple trees I admire.
But friends of mine question this. They give examples in various poems of different poets, like 坐爱云林泉石好（欧阳詹）, 坐爱青草上（孟郊）,坐爱前檐前（白居易）,坐爱溪上山（萧镃）,坐爱木兰舟（程敏政）, etc, where 坐 could not have meant 因为 but only its original meaning "to sit".
I think my friends make more sense than my teacher.
“When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I choose it to mean — neither more nor less.’
’The question is,’ said Alice, ‘whether you can make words mean so many different things.’
’The question is,’ said Humpty Dumpty, ‘which is to be master — that’s all.” ― Lewis Carroll, Through the Looking Glass
Teacher is right! I found this:
对于古诗的理解，可以说是“一千人心中，有一千个哈姆雷特”。
杜牧这句诗想表达的是：停车是因为喜欢傍晚枫林的景色，所以停下来欣赏。 What Du Mu with this line of the poem wants to express is:
停车是因为喜欢傍晚枫林的景色，所以停下来欣赏。
I stopped the wagon because I like the evening maple forest scene, therefore I stopped to admire it.
既是表达“因” 的意思，
If Du Mu wanted to express the meaning "because",
为什么杜牧要选择用“坐”来代替？
why would Du Mu want to use "sit" as a substitute?
有相关专家表示：
There are scholars who say:
因为这首诗是七言绝句，
Because this poem is a seven word quatrain,
本身要符合七言的标准；
it must keep to the seven word standard;
如果“停”字后面用“因”，
if the character "stop" is followed by "because",
平仄是对不上的。
the tones will be wrong.
而“坐”字能对上仄音，
However the character "sit" fits in with the oblique tones.
所以才会用“坐”来代替。
Therefore (Du Mu) could only use "sit" as a substitute. (for "因")
事实上，杜牧并不是第一个用“坐”来表达“因为”的人。
In fact, Du Mu was not the first poet to use "sit" to express "because".
早在《陌上桑》中就有一段：
Previously in《Mo Shangsang 》there is a passage:
“耕者忘其犁，锄者忘其锄。
"The ploughman forgot his plough, the hoeman forgot his hoe."
来归相怨怒，但坐观罗敷”。
Coming and going they are angry and blame each other, just because they were watching Luo Fu.
这里的“坐”便是“因为” 的意思。
The meaning of this "sit" is precisely "because".
杜牧"坐"
坐 (汉典)
介词，因，由于，为着：“停车～爱枫林晚，霜叶红于二月花”。
副词（①空，徒然，如“胡为～自苦，吞悲仍抚膺”；②无故，自然而然，如“如若此，则盐必～长十倍”；③遂，即将，如“寒英～销落，何用慰远客”；④深，如“感此伤妾心，～愁红颜老”；⑤正，恰好，如“西村渡口人烟晚，～见渔舟两两归”）。
For this particular sentence the general consensus is that 坐 means "because".
A little bit of history of how 坐 (to sit) came to mean "because":
The oldest meanings of 坐 are "to kneel" (跪), "to sit", or "to be fixed at some location."
During the Han dynasty, "坐" came to mean "to be punished according to some criminal law". This is where the meaning of "because, due to" began to emerge. 《助字辨略》 gives the following explanation: "汉法入罪曰坐，言罪与律应，不得移动也。" (In the laws of Han, 坐 means to be found to have committed some crime. The connotation is that the criminal status is ascertained by the law, and cannot be removed or changed.)
An exemplar is 《汉书 贾谊传》: 古者大臣有坐不廉而废者。 (In the past there are officials who are demoted due to corruption.)
Over time, the criminal connotation of 坐 became weakened, and its meaning is generalized into "because, due to", as in the poem 《陌上桑》: 来归相怨怒，但坐观罗敷。
One possible explanation- Because 陕西话 (Shaanxi Dialect) used to be the official Chinese language in the past for a period of time. 长安，现在叫做西安，是唐代的首都。此诗写于唐代，可能使用了长安的官话，与现代陕西话有相似之处。坐爱可能源于陕西话里的Zou Ai （zou爱,just because I love)
