Mold in the GU bathroom refuses to respond

Maybe here someone is confusing a developer with a construction company/turnkey contractor? A developer is not obliged to let anyone in, as it is their property until full payment is made. With a construction company/turnkey contractor, it’s different.

Our turnkey contractor does it the same way: a master key in the front door... each craftsman then gets one of those. Why the client doesn’t get one: often several houses of a turnkey contractor are built in one area. If they were to give the key to the clients, they would have unauthorized access to other houses. The craftsmen are authorized and move around the houses according to logistics/construction status. As a client, you can enter the construction site during the day... that’s the note when the turnkey contractor objects.
We received a key from the turnkey contractor: we built independently, away from other construction sites.

As a client, I would not care about that at all. What if I want to provide my own labor?

One can go to the construction site during the day as the client... this is the note in case of objection from the general contractor. We received a key from the general contractor: we built independently, separate from other construction sites.

That is indeed an argument, but actually not acceptable from the clients' point of view. The larger general contractors known to me (in the prefabricated house segment) hand over the keys to the clients already on the first day, although all other sites with addresses are theoretically known. Nevertheless, one must of course not enter other sites without permission, even if one has the key for them.

Landlords, for example, also have the keys to the rented properties, but naturally may not enter them without permission.

We built with a local general contractor and immediately received the key for the construction site (our house). Our GC used the same lock for every house. All subs had a key so they could enter every construction site. We could have done the same and entered any construction site. Where is the problem? Expensive tools or something like that were never left lying around; the subs packed them up at the end of the workday. I doubt there is a big risk here that homeowners would steal stuff from their own or other construction sites.

I wouldn’t accept not having access to my own house. After all, you want to walk through the construction sites calmly in the evening and enjoy (inspect, document, photograph, ...) what happened during the day. Doing your own work isn’t possible in parallel either. Maybe the GC wants to prevent that; simple stuff is often sold expensively here (like pulling network cables, for example).

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After all, one wants to calmly walk through the construction sites in the evening and enjoy (inspect, document, photograph, ...) what happened during the day.
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When I see what we alone have had to complain about—or at least discuss—during our renovations in recent months, I actually don’t want to know (but actually do) what needs there are on a new build.
In my opinion, someone impartial and "professional" should and must monitor and document the whole thing every day.

Our general contractor also had the same key for all houses. Still, each client had their own. (I think I even still have the construction lock and key today, only our general contractor no longer exists)

What surprises me is that general contractors do not switch to electronic locks. That way, the client can only enter their own house, but the craftsmen can enter all houses. In cases of liability, there might also be proof of who went in and out and when. The locks can be taken along. Maybe it also has to do with the construction dirt, making the locks unsuitable for that.