Think about it from the Founder point of view. Very few startups are 8x5. Most expect you to put in a few extra hours, be on call, etc. By letting them know if you've got a side project you plan on dedicating yourself to you are taking those hours out of that pool.
If it's just for an Open Source project, that that's one thing, but if you're also working 10 or 20 hours a week with another company then they (a) need to know that they have to account for that in scheduling and expectations and (b) want to know that you're not working for a competitor and passing inside information.
I had one guy on my team who was working 16 to 24 hours a week at another job, which meant that needed to be careful how I scheduled him (because at the time we didn't have enough work to schedule everyone full time. If we had, well then he'd have to sort that out).
It's not really predatory, or at least not in intent (you always have exceptions).
The basic rule of thumb when seeing stupid clauses like this is 'Someone did something shift, a lawsuit happened and the words "I didn't know I couldn't" came out of the defendant's mouth and that cost/almost cost the plaintiff the case. So now they make it overbroad so you can't claim you didn't know'.
There have been several cases over the years--one of which got several cow-orkers of mine fired--where the "side project" turned into a real company and it turned out to either be based on the companies source code, or created by looking at the companies source code (in one case a competing product, in another case a complementary product).
In some ways it's an "anti-predatory" clause.
I've mostly been subject to it at much larger companies and defense contractors.
It's also something that you can usually get a 'waiver' (or whatever your company calls it) for. Go to your boss, or whomever and get them to put in writing that "Yeah, we know about this, and it's ok with us".
If it's just for an Open Source project, that that's one thing, but if you're also working 10 or 20 hours a week with another company then they (a) need to know that they have to account for that in scheduling and expectations and (b) want to know that you're not working for a competitor and passing inside information.
I had one guy on my team who was working 16 to 24 hours a week at another job, which meant that needed to be careful how I scheduled him (because at the time we didn't have enough work to schedule everyone full time. If we had, well then he'd have to sort that out).