Good point but I don't think quite right.
I think it's the housing affordability issue (hinted at earlier). Stay with me here.
In the past, adults could grow up and leave apartments or condos or tiny rented places with no yard or shared yards and buy their own 3/2/2 to settle down, start a family, whatever. Then they would have babies and/or buy pets. They had the appropriate room and services to accomodate them.
With housing being such a crisis (e.g. starter homes almost non-existent, another thread), more "kids" aka young adults are staying in apartments and multi-tenant living a whole lot longer. Maybe until their middle ages and maybe forever for all I know. So there is no more waiting until you buy a house and next phase of your life which includes a pet, but rather, if you want a pet you have to get it in suboptimal living conditions.
So then you buy your best friend and now have a pet that lives in 500-1000 sqft area without an easy access yard or even patio sometimes, landlocked between hundreds of other 500-1000 sqft rooms, anywhere from 1-5 stories up.
Because of this, pets probably dont' get as much exercise or outdoor time (I mean, the owner tries but it's harder to take the elevator or walk the flight of stairs and meander down to the tired patch of grass all the other pets have trod over, multiple times a day) and so owners rationalize that it's lucky bit of synergy. They need to run errands (HEB, restaurants, etc.) and the dogs need to not be locked in a soulless apartment, so why not take them with them.
Seems right to me, at least. Maybe dog owners who live in apartments and can't afford housing (if any post here) can confirm or deny.