That is a good point. Normally, if you use a web service to make a map then there has to be some standard boiler plate kind of license for the website owner to use your uploaded material in order to be able to make use of it. So this is kind of normal. But the license to make derivative works from your upload is certainly not standard.

You should note the terms of service for this website too which states flatly that content uploaded by members is owned by the member in question. But it too has a clause in it to allow use for the website promotion. I am not certain how often the guild posts maps outside of the forum but I do know that there is a guild facebook page and maybe there are other similar social outlets. I guess sometimes the annual awards might be the sort of thing that make a news story and we had interviews with our best cartographers a while back. So there is some limited scope to post images uploaded to the guild. But they are never sold nor is there any option to make any kind of derivative copy for commercial purposes. There has been talk for several years about making guild calendars with 12 great maps in them but the art in one would have to be licensed separately with each artist for that use.

I suspect that there is no intention from Inkarnate to do derivative copies either for the purpose of selling artwork but probably only to resize the image to show. But it is worth knowing those terms and its likely that all cloud / web based tools would have some similar terms to them.