Why exactly would they be commanding their own ships? Certainly Scott would insist "I'm an engineer, not a starship captain." And the others haven't done much to distinguish themselves from the many other Starfleet officers doubtless vying for command positions...
Scott became Captain Scott so he did get his own command. Off screen the other characters probably did distinguish themselves just as much as Sulu, who got his own command. Chekov was XO of the Reliant in 'STWOK', one heartbeat from the Captaincy. Spock was promoted to Captain by then as well. He never desired commanding an exploring ship, whether that was due to the personality of the character OR Shatner not wanting to be upstaged by Nimoy as Captain of USS X.who knows.