I've never been but I think the site below helps explain why most visitors choose to visit as part of a cruise - there seems to be a lot of bureaucracy to deal with, which is understandable given the environmental sensitivity of the archipelago.

https://www.galapagos.org/travel/travel/planning-a-trip/

While I would love to visit I don't think I ever will because of the environmental impact of the huge visitor numbers - 30,000 permanent residents but 200,000 visitors a year doesn't look like a sustainable ratio to me. Shades of what's been happening on Skye this summer.

https://voices.nationalgeographic.org/2015/01/05/galapagos-tourism-backfires/