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You spend way too much for service, that's the difference.

I'm currently spending a flat $17.50/month for three cell lines, with no taxes/fees on top.
$80/month for 4 phone, 2 current year(getting bill credits) and 2 previous year (paid off) devices, 4 apple watch cellular lines and home internet is too much for service?

Actually my current bill is -$3 because I still have a bill credit from a 3 year old device.
 
The best time for the carriers to attract new business is when they are selling a new phone and I presume kick-backs from the phone manufacturers. Second best time is when someone already has a phone that they want to keep using. Probably why it's this way.
I generally buy a used version of the oldest/cheapest phone to trade in for max dollars. For TMo this year I expect it to be the 12 pro for a 16 pro "on us". Then I will pass down my 15 pro and sell my kids 14 pro. Take the net proceeds from the 14 pro sale after accounting for the 12 pro purchase (usually $200-$250 net) and apply it towards the monthly bill for TMO. Can't pay the phone off early and get the credits still anymore, but you can apply it to your service plan and effectively get the same benefit. Keeps me in a negative balance for my 4 phone lines/4 watch lines and home internet nearly 100% of the time.
 
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