Why don't members who left during the year get K-1 forms?

If the withdrawing member left and was paid out in the same year, they should absolutely receive a K-1 for the year.

If the withdrawing member was paid out in a two-part withdrawal, with the first part in the previous tax year and the second in the reporting tax year, that member does not get a K-1.

For example, a member's withdrawal is announced on 12/1/2022, then paid out on 1/15/2023. That member should have received a K-1 for the 2022 tax year, but not for the 2023 tax year.

Note that the previous year's K-1 for the withdrawing member should have been marked "Final Return", which can be checked by hand.