I didn't downvote, but I'm fairly certain the downvotes come from the "you're thinking small" part - it comes across as condescending, even if it wasn't meant that way. If the parent chopped off the first sentence it would dramatically change the perceived tone toward a neutral to positive one. That is, the first sentence is largely unnecessary (it adds nothing other than the risk of people taking it quite negatively).
Like so:
It is wonderful to bootstrap an app and make income. However some ideas are much larger and need a big team and years of effort before the big payoff.