Part of asking me to give you a commendation is asking me not to give a commendation to the other players. So there's a risk of such a request coming off as grabby, childish, or selfish. And if it feels like that, I'm probably less likely to give you the commendation.

That said, I imagine if a player had been really enjoyable to play with and found a kind and humble way to ask for a commendation at the end, that might sway me to give it to them instead of another player in the same group that I also really enjoyed playing with. Like maybe if they were like "I'm 10 comms away from finally earning my (insert reward here), so if you enjoyed playing with me, I hope you'll consider me for a commendation!" Maybe.

But truthfully, the best way to ask for a commendation is to just be enjoyable to play with. Putting effort towards your glam, your portrait, and your friendly banter will go so much further towards making me want to commend you than holding your hand out and saying "comm pweese!"