Based on my experience, it's very hard for people to accept something new in the first place, for example, when WP was introduced. And this is still happening now. Once a group of people accept a new concept, building on top of it to improve the system is a little easier.
OK. Thinking about it, there might have been a market there all along, but how come no one served it before? I mean Jason is crazy brilliant (talk to him, it's an experience!), but surely others could have come up with the same idea - right? I guess we'll never know, but my guess is that not too many people went out and searched for a thing like WPEngine before WPEngine
There are 75 million (!) WordPress sites in the world. It would be amazing if any software platform with 75 million users didn't have a large number of consultants available to help people with it.
In a nutshell when he was building WPEngine he went to LinkedIn and found folks who were Wordpress consultants. He then sent them a follow email and said he's building a product for "folks like you and would love to talk to you about your pains, needs, etc" (customer development stuff) and offered to pay for their time. It worked well - he sent 40, 100% agreed to talk, actually talked to 38, and 0 asked for money. He suggests this worked so well because the offer to pay showed he was respectful of their time so they were happy to help. YMMV.