There are pieces of information that have to be gathered and manually calculated and entered into a system to get a full set of W-2's generated.

Best example - personal use of company vehicles. If you work somewhere that has company vehicles, and those with them can use them for personal use, i.e. commuting to/from work, that has to be determined "outside" of the system and put in. That's a taxable amount.

It's like pulling hen's teeth to get that information from some people, getting them to estimate (actually they are supposed to have logged) the amount of mileage that was for personal use. Hence, the delay most times.

There are also other things, executive comp plans that might include some insurance benefits (life, etc) that others do not get, that has to be manually entered. There are quite a few things other than just weekly/monthly pay, that go into doing some W-2's.

A company isn't going to run W-2's in two batches, they're going to do them all at once.

And, some places just sit on them until Jan 31, just in case they find something wrong, that they've missed.