[kkt262]

You're relying on someone else to build the core of your business. While it works in some cases (maybe yours), there are many problems that can arise. For example, it could be harder and slower to iterate new versions of your product. It can also be expensive, and as a startup you want to keep your expenses as low as possible.

A friend of mine had outsourced development and later on that dev team said they wouldn't finish the product unless they take 50% equity of the company. Of course this happened because he had very little experience outsourcing, so if you have found a reliable team to do your work then it's fine.

I just think incubators are worried about it because a large majority of the time it doesn't end up working.

As far as single founder goes, I've found it invaluable to have a co-founder. Even just for the emotional aspect and to keep each other accountable for the work is an important part of having a co-founder.