Youtube had a space devoid of competition. The next guy doesn’t. If the next guy wants to compete, they have to have all the features of Youtube or people will complain. Many of Youtube’s current features cost money and weren’t present when Youtube started.

The space is also more regulated now that Youtube exists, meaning the new guy has to follow regulations which normally costs money. When Youtube started, those regulations didn’t exist, because Youtube didn’t exist.

Youtube got big by building a city in an open field surrounded by nothing but open fields. The next guy has to build a city directly next to Youtube, follow all the same laws as Youtube, and ask you not to drive into Youtube.