Why are Bitcoin miners not speeding up and expediting the confirmations? Is it for personal gain? in that case that means Bitcoin is centralized and not decentralized because miners can control its fees?
There is no way for them to "speed up" or "expedite" confirmations... They have hardware running to find a sha256(sha256(block header)) that's under the current target. It's not like they can increase the target by themselfs, this will only happen if the average time between blocks is > 10 minutes, at this point the difficulty will be decreased and the target will increase at the next difficulty adjustment.
If you look at any block explorer, for example this one:
https://blockstream.info/ you'll see that the last 10 blocks were completely full (out of the 10 blocks that were shown).