Two pet theories I have about this

1. it is profitable for big chemical companies and whatever lobby makes the lawnmowers and weed whackers for everyone to have these big lawns that need to be maintained via mowing and pesticides. There are breeds other than bluegrass that don't grow that tall, chiefly buffalo grass, with deeper roots that make it generally more healthy, less patchy, less susceptible to weeds, etc.

2. It is convenient for the ruling class that we have to do all this maintenance individually, leaving us less time (and wealth) to organize and build community/alternative modes of governance. Divide and conquer and all that.

OK I lied here's a 3rd:

3. Western society is pretty much defined by our need to control nature/the world around us in outright denial of any consequences that might arise from doing so.