why can't I still access a new meeting?

Hello. It has to do with your license. You can only host one meeting at a time if you have a free/basic account or Pro license. Even if you start one meeting and assign someone as the host, that is still your meeting. So, you can't leave that meeting and start another meeting as host. That meeting would need to end before hosting the next meeting.

If you have a Business, Education, or Enterprise account, you can host two meetings concurrently, but that account type is required. Here is Zoom's support page regarding hosting two meetings concurrently. https://support.zoom.us/hc/en-us/articles/206122046-Hosting-concurrent-meetings

Please let me know if this answers your question. Thank you.