You're barely given any scores for doing support duty (except for healing) or debuffing enemies, and nobody wants to sacrifice their progression speed for the greater good. This is called bad game design, not bad players.
On another note, reworking fleets has been requested many times in the past, they just ignored it. You know why Veteran and Legendary worked well beside each other back when there were enough high tier players to play both of them? Because there is an overlap: Tier 4. It can join both, and is excellent for mitigating issues with the grind.
Same thing needs to happen at lower tiers, but they don't care. Actually you can't say anything to these guys that conflicts with their broken ideas about the game, they don't listen to feedback, even if it's constructive.
As it was suggested - a long, long time ago, in a galaxy far, far away - the fleets should be changed around like so:
Newbie Fleet (new, though not an actual fleet, doesn't really need a matchmaking queue):
Tier 1 only, plays against bots, may be restricted to proving grounds only. Really just for tutorial purposes, and to get ship lines started.
Tier 2-3, already has access to all current game modes, bots are only used if absolutely necessary. Officer Briefings are forced inactive on all ships.
Tier 3-4, has access to all current game modes, no bots ever. OBs active.
Tier 4-5, has access to all current game modes + Team Elimination, no bots ever, OBs are active.