Having my credit card already is an overwhelming advantage for the Apple App store and for Steam. I won’t say it is impossible to overcome, but I think I could count on my fingers the number of instances where I, like, typed my card into a website to buy anything, in the last decade.
Yes, but they are mostly paying little or nothing. How much did you spend on phone apps this year? And ads pay a pittance, unless you have massive scale.
I'd wager there are more people paying for software for their smart phone than any other platform they use.