I had never seen anyone use the punctuation the way you do and it inspired me to do some Googling.
Lo and behold, it turns out that there ARE some cases when you are supposed to precede the word "but" with a comma (if you are connecting two independent clauses). I did not know that.
So this is correct because it connects two independent clauses.
But these are not two independent clauses so this is incorrect.
I had no idea that rule existed. Is it not enforced or have I just not been noticing? I can not recall ever seeing it before.
And what's even more fucked up is that
there ARE some very rare occasions when using a comma before "because" is correct. Well fuck me running. Mind blown.
This is not such an occasion.
Nor is this
But there ARE some occasions where it would be proper.
Huh... Well, I guess you learn something new every day. I'm not going to start using either of those rules any more than I am going to stop using Oxford commas but it's good to know they exists.