Simple truth is, county cricket is now completely designed to produce one day players. That means that spinners will be rare and any that come about will generally be one day style spinners. People can argue but the fact he majority of batsmen playing 4-5 day cricket now are all one day style players just proves the system is wrong.
What county is going to develop a cook style player when the majority of cricket anyone plays now is hit and biff. Spinners come into their own in long games, if you aren't playing any then you won't develop the skill.
Moeen is crap but given England seem to want his batting more than bowling expect him to stay for a few more years yet.