@Sir Yasheen
Blackbeard didn't get his increase because he defeated Bia Hancock, given he had his 3.996 billion bounty at the time he was fighting Boa Hancock.
He mostly got it because of Kuzan (who doesn't seemingly have a bounty yet and I think there was a SBS or something like that which implied Kuzan in Blackbeard's crew was rumors) and because his crew became stronger with all of them having devil fruits now.
To answer the topic, Luffy's bounty is already too low for what he did. But we know the WG tries to hide Luffy's true threat level, hence his low bounty.
Luffy, after Egghead, shoud have gotten an increase because he and his crew fought an entire Buster Call consisting of 100 navires, 9 Vice Admirals, 1 Admiral and the Gorosei and they managed to flee and an entire island got destroyed in the process. That's not a little feat.
But if we stay in this logic of the WG trying to belittle Luffy's feats, we can say the WG splited up the accountability between Luffy and Dorry/Broggy, hid the fact Luffy "won" against that huge Buster Call and considered that setting ablaze an island is a low level feat for an Emperor like Luffy. So no increase for Luffy.