The 'Milner Conudrum'. It is quite common what you felt. Backup positions at top teams are mostly for aging legends looking for a last trophy and young up and comers who are trying to make a name. No middle of their career player wants to ever be a backup. Imagine if Robben and Do Maria had chosen to stay at Madrid and be backup when they could star at a slightly lower level.I'd like to chime in on the 'they'll be happy if we win things' POV. It's total bullshit and I'm speaking from experience. I played travel baseball and AAU basketball (think academy level) from youth until my late teens. I was on the best teams in the state (hundreds of teams) and was the 10th or 11th best out of 12-15 players. I didn't play often and when I did it was vs garbage teams or I'd come in late in blowouts. On paper I played 3/10 games which isn't terrible but in reality I basically didn't add anything to the team and wasn't trusted in the vital moments. You aren't happy to win things, you're embarrassed and humiliated. You feel like you aren't good enough to be at the highest level (what every serious athlete needs to believe to maximize their chances).
It would piss me off when the coach would throw me in for the final few minutes in a blowout (think Sterling being put on for 5m in a 2-0 game). That's really not doing much positive for him psychologically ... but he gets a game on the stats sheet. I 'loved it' when Carlitos told Bobby Manc to F off, I'm not warming up, in the CL because that's what many of the second choice players dream of doing.
My final two years I dropped down to a lower rated squad and was the best player. We didn't win as much, which is never fun, but I felt valued and 'more alive' and that's more important than winning when you don't contribute much. It feels 'fake' and not as enjoyable as it appears on the outside.
Am I an outlier? I don't think so but if you think 'it's cool...they are fine, they are winning things' ... well then you're just lying to yourself. You can't be vocal or outspoken about your unhappiness in the situation because it's a bad look for yourself and comes off as a poor sport.