Core doesn't support segwit in full yet.
Core has merged bech32 addresses so with current version it should work to send to and receive from bech32 addresses.
I assume that everyone can receive from bech32 but older wallets can't send to them as they are invalid for them.

I like on chain optimizing so Bech32 isn't bad but who knows about Bech32? Maybe 0.1% of the Bitcoin users? Probably less.

And as said earlier, services often use bitcoind for their transactions and as long core doesn't support it in full they can't support it without a lot of development.
And even if services switch to Segwit then still not every transactions is segwit.
Coins already on services aren't in segwit addresses and moving them first to segwit to do segwit transactions increases the cost for services.
Adoption would start with offering deposit addresses for segwit and then some transactions will be segwit and some not till all coins are naturally turned over.
On the first step users could save a bit in fees on deposits but not on withdrawals on most services.
Hardfork with flextrans + bigger blocks would have solve all current problems and still would allow sidechain development.
This one was the worst solution with segwit, Till the time Segwit adoption comes closer to 100% the blocks will be full already also with Segwit transactions...