Also, we had memory slots on '90s cards. They were extremely expensive and proprietary. Ever saw a Matrox VRAM card? I never did.
PCI is (was) allowed to be even longer. Old AT and ATX cases had a slotted support bracket to hold the far end of the PCI cards. See how an Adaptec 2400A looks like.
Like the M.2 connector?
> Data lines need to be longer
Like the data lines going all the way to an on-motherboard storage device?
Yes, though likely something with a higher pin count since memory access is more likely to be random and can be parallel versus block storage.
> Like the data lines going all the way to an on-motherboard storage device?
Yes. Why would a GPU manufacturer/packager take on that cost, if it’s presently served well enough for most people by offloading it onto other parts of the system?
This is why there are several proposals of improved forms for memory modules, which use different sockets, like LPCAMM2, which should be able to work with faster memories.
However even LPCAMM2 is unlikely to work at the speeds of soldered GDDR7.
Moreover, when you do this manually, unless it is something that you do every day it may be quite difficult to be certain that soldering has been done well enough to remain reliable during long term use. In the industry, very expensive equipment is used to check the quality of soldering, e.g. X-ray machines.
So unlike inserting a memory module in a socket, which is reasonably foolproof, soldering devices is not something that could be used in a product sold to the general population.
When I was young, there still existed computer kits, where you soldered yourself all the ICs on the motherboard, so you could get a computer at a much lower price than for a fully assembled computer. My first PC was of this kind.
However, at that time PCs were still something that was bought by a small fraction of the population, which were people that you could expect to be willing to learn things like how to solder and who would be willing to accept the risk of damaging the product that they have bought. Today PCs are addressed to the general public, so nobody would offer GPU cards that you must solder.