Could you elaborate a little about which problems may I expect if using sockets?
Mechanically it needs more care. It is easier to bend or break a pin on insert, or miss that a pin is not inserted at all but dangling on the side. It is much simpler to put an IC directly into the PCB without errors than to push it into a socket. If you have experience with this, there will be no issue, but the kit is optimised for effortless builds even for relative beginners.
It may not seem like a big deal for 1 kit, but consider this: if the IC insertion success rate is 99%, it means the remaining 1% cause a problematic build, and a bad experience, for one third of the kits... That is a support load we won't be able handle. And then: those builders who really want them often have their own preference for a specific type, usually the more expensive milled ones. So better leave it up to the builder to decide what to do here.
The big two chips are a totally different story, so we added them there.
