It's part of it. Another part of the reason is patent related royalties that they have to pay to the likes of Qualcomm, Nokia, etc. for any device that has a working 5G stack inside of it. Apple actually has had their own 5G modem implementation for a few years now; they clearly have the technology to deliver this with a clean full in house chip design.

But any device that has that embedded would have some royalty overhead added to the BOM. Which is why they've always had ipads with and without 5G and have so far never really bothered with adding this on laptops (which actually would make a lot of sense from a technical point of view). Operators would probably love that because it's a nice up-sell opportunity on monthly subscriptions. And with soft sims there would not be a need for a hardware sim card.

For the same reason, you don't see this feature on many other laptops either. There are a few obviously but it's a less common feature than you'd expect given how important good connectivity is to most laptop users.