Indeed, I'm just see it in my perspective but for big exchanges; they could save Million dollars fees within a month, a week, even every single day. There are few wallet developers which has been implemented P2SH-P2WPKH address as far as I know, such as Ledger wallet, bitcoin core, samourai wallet (on developing), and electrum 3.0. Ledger wallet is the first one I guess and electrum implemented segwit address after 2 months, not sure why this latest upgrade for segwit support is taking so long.
Bitcoin core has a working segwit support since 2016 (of course then working only on testnet). It was not included in the stable versions because before segwit activation, users would lose funds. Electrum added initial segwit support in January 2017. Electrum delayed segwit in stable versions because of interoperability issues (importing segwit keys is not completely standarized) and adding segwit support to hardware wallets.
Bitcoin core was supposed to have segwit GUI in 0.15.1 but they had to work around these stupid Bitcoin forks (code for disconnecting B2X nodes had to be added first). I'm pretty sure exchanges also spend quite a lot of man-hours on these forks and segwit is no so pressing. So maybe these crazy times of Bitcoin forking, segwit support will start to roll out faster.