Please help me understand why every year or two we must be forced to purchase – Glen Post email address

Marc sent a message to Glen F. Post, III President and CEO, CenturyLink, Inc. – email address that said:

Please help me understand why every year or two we must be forced to purchase new modems to work on your service because it degrades over time. Every year or two we must spend 75-150 for a modem to be used on your service, which I pay approx 500.00 a year.
I do not feel that it is in my best interest to continue this service if we must be forced to purchase modems.
Sincerely,
Marc