The Gemini protocol is intended to exclude features that could be used for tracking. It has no cookies, user-agent, referer, etc and the protocol is not extensible enough that such features could be easily added.
Also, frankly, the spartan design of native Gemini pages (very limited formatting, no scripts or even inline images!) means that the circle of nerds who use Gemini will almost certainly remain too small to catch the eye of ad-tech. It's hostile to commerce in a way I find kind of delightful.