Trading is a whole different game from exchange operations. Exchanges make money by charging a small transaction fee on each trade, regardless of the direction. So their whole business model is securing volume (i.e. number of traders), which requires domain expertise in marketing, security, partnerships, and technology. Whereas a trader's only interest is making a winning bet, so the only domain expertise required is market analysis.

There's a reason white-label exchange source code is only $10k. Requires millions more to actually make an exchange a successful business.