That´s a question I´ve been pondering over for a while now. I´m also not really a mobile gamer, I mean I´ve played some for some time but that´s about it. The reality is, a mobile game usually has very short development times.
This has some interesting benefits. Imagine you have 1 year spare time, no day to day job, you are a solo-dev:
In 1 year, how many mobile games do you think you can make? Probably 6, possibly more. But let´s assume you make 6.
In 1 year, what kind of game can you make for PC? Is a year even enough time? Of course this also varies on the type of game etc. but lets assume your scope isn´t super-huge and you make 1 game. (As a reference: Dust - An Elysian Tail was planned to take 3 months but ended up taking over 3 years, made by a one-man-army)
So, same timeframe, but on mobile you pushed out 6 games while on PC you made one. And lets be real, there is NO guarantee that any of the games you made will be popular. BUT on PC you only have one shot, if this one game flops... well that´s it. On mobile, if 5 of the games flop you still got the 6th. In other words, your chances on mobile are better than on PC to make something that a lot of people will play.
And about money... the thing is it is kinda required to have. Most people (like me) have to go to work for it. This means less time to work on games, working on games... after work. I don´t doubt there are people who can do this with long-term-projects but unless you are leaking dedication out of every orifice it is unlikely. I´m not the type of person that can do this. A mobile game on the other hand... it seems so much more doable in it´s scope. And if it´s a Hit, it will open up the opportunity to really follow the passion.
So if you make your one big PC game and it flops... what are you gonna do? Maybe you satisfied your passion with it, that´s fine, but you still need money to pay your bills afterall. That´s why I´d say... chase the money, then use the money to chase your passion.
An interesting quote from Walt Disney in that regards