One key difference is licensing. As a physician you have to take the USMLE Step 1,2,3 and then potentially other board certifications. We engineers don't have any of that.
Yep, I agree about limited industry but it does work in that respect. I see it used a lot for content creators as a way to organize and tier out their fans as well.
IMO its a good competitor to slack. They probably make money from businesses too. They have lots of options for permissions/roles and all kinds of API access to write bots for.
Sports are a business and fall under entertainment anyway in my opinion. Owners make a lot of money and you won't see them footing the bill for new stadiums/fields generally too. Thats all tax-payer funded in the US. Internationally I'm not sure but I doubt they are footing the bill 100%.