Asking this because sometimes I also wonder if I should open source my project, but I have my doubts on how much you can gain from it (apart from the nice feeling of contributing to open source ;))
Contributors is easy to judge, but the second bit is not. It includes people you'll never even hear from.
For me, the big question I ask is basically "What are the chances this software becomes unavailable in the future and what's my escape plan?" These two weigh against each other -- if it's a non-critical tool and the plan is "go back to doing it the old way, with near zero business impact" then I don't really care about the chances it disappears a whole lot. If it's "Start a several-months migration effort while the business is crippled" then suddenly that first bit becomes incredibly important.
I consider chances a small (especially one-person) company disappears is fairly high. Same for a VC-funded startup (along with the chances they kill or pivot away from the product, which is effectively the same thing).
Open source means it never really becomes "unavailable": It might be costly (eg if I have to fund maintenance on my own) but it still provides low risk of crippling my business.
When I'm considering new software, the non-OSS stuff run by small companies just naturally goes to the bottom of the list for exactly this reason. If I go with something higher up on that list, that company won't even know they were being considered, let alone why I didn't pick them.
It's more the feeling for me, yes :)