The reason is very simple,people can not use something if service provider(wallets,exchanges) do not support it.Unfortunately almost all the wallets/services working on it quite slow and we do not see any bigger results.Two most famous hardware wallets Trezor and Ledger have support for SegWit for some time,and most used desktop wallet Electrum enabled SegWit in version 3,but this version have problem with Windows version 7&8.
There is a list of wallets/services on BitCore site but it is not updated for some time :
https://bitcoincore.org/en/segwit_adoption/I hope that we can see more support for SegWit in next year,and also Lightning Network.With this full enabled transaction should be fast&cheap.