It matters because the UA program is good but the only way to get status is to spend a lot on flights. This is not a problem if someone else is paying, but it's a problem if I'm paying.

On the other hand, you can be EXP on AA without spending any money on flights at all.

Earning miles and LP through other (cheaper) methods and using the miles to fly for free is a good method if you would have to otherwise pay for your flights, but it's not worth much if your employer pays for your flights anyway. I expect to have about $1000 of spend on flights this year, and still requalify for EXP. All my other travel was / will be with miles.