Why charge a upgrade fee?

I've been a mobile customer for well over 20 years, AT&T for a couple of years, then Verizon for most of the time and just recently moved over to T-Mobile.  I have never paid an "activation" fee for a phone.  What a crock.  I say waive that fee or I will go to another carrier, and they say okay.  Maybe it's because i have good credit and the carriers want those customer to stay or come on board new, but they never say no or even argue with me, they just waive it.  Since I like free budget phones as well, I can usually wrangle one free every 3 years as well.   I do pay tax on the phone of course, and I have to stay with the plan for 24 months, as they usually credit me each month for the cost of the phone.  You have to be willing to change carriers though.  That's how I landed here, Verizon was starting to charge me more, trying to get me out of my grandfathered plan and move to a bigger plan.  I said no and they said sorry, so I joined up here.  I get far more in data, perks, all at a $20.00 month price reduction.  I've read Verizon lost all most 130,000 customers last quarter.  They really need to rethink their business model and start to get competitive again.  Right now, they are the most expensive and seem to give you the least for your mobile plan dollar.  I also read they are laying off 6000 customer service reps here in America and sending those jobs overseas.  That won't make Verizon customers happy.  Sign of the times I guess, gotta pad the bottom line for the share holders.  I'm happy here at T-Mobile and switching from Verizon was painless for me, thanks to the brilliant sales lady in the store I went to.  I didn't want to try and port the number myself.  She got it all done in about 15 minutes.