One reason is because there are more tools available to create online marketplaces.
For two-sided marketplaces, people can use Sharetribe, WordPress (with plugins) or hire developers to create their marketplace.
Other factors include:
- The costs are getting lower
- Shows like Shark Tank & The Profit are making it seem easier
- People are now more used to having hundreds or thousands of followers. I feel this leads to the perception that they could attract this same amount of people to use their product.