Lots of trouble with shops improperly servicing transmissions and damaging them. I wonder what causes that.
Not sure if your question was rhetorical or NOT. But, trans are more complicated and sophisticated today than yesterday, they have more and more innovative and "different" components and mechanisms than the past.
Lots of shops buy into aftermarket shop tool hype, selling trans flush machines, etc. The machines might have worked with older, simpler trans, but today, the could cause fluid starvation, pressure or back flow problems and damage a trans.
If the manufacturer recommends against flushing a transmission, you shouldn't do it. Sadly, you'll find even Dealerships using these machines even though the FSM they are suppose to be following, say NOT to use them.
Yes, the temptation is there, you would like to change all the fluid in the trans with all fresh fluid when you do a trans fluid change, you can't, half the fluid remains trapped in the transmission. That is why the manufacturer recommends a schedule of changing the fluid with that in mind, if you keep changing half the fluid often enough, there will be more than enough good fluid to keep the trans operating just fine and lasting more than long enough.
The trans is NOT designed to pump the fluid out or have new fluid pumped into it as its operating, something goes wrong with this pumping of fluid in/out, or the trans has different circuits or valving than others, it could damage the trans.