Fly United, Or Not

[travel, United Airlines]

So here is my latest frustration – trying to fly to UK this summer and
use Frequent Flyer miles to upgrade from Coach to Business. Sounds
simple, no?

No. It isn't. First of all, only some fares are eligible to upgrade.
Second, you may be willing to pay the (2x higher) fee but UAL is
holding out for people paying the full Business class price and
doesn't want my money. Well, to be fair, they want the money, they
just won't promise me an upgrade NOR pay me back the difference if I
don't get said upgrade.

So, we sit and wait and wonder why I have 100,000 miles in an account
that are looking more useless everyday.

Exactly how is this making them any money and encouraging my loyalty to them?