Personally I don't have a problem with it but I imagine Edna the 76 year old poll volunteer might have an issue or two.
Could you explain why someone who is working 2nd/3rd shift doesn't have time to mail in an absentee ballot when not on the clock?
The proposed law doesn't say anything about closing because of staffing shortages. Rather, it makes it a blanket policy that it is illegal to open polling places before 6 am or stay open later than 9 pm.
In regards to your question, there are several answers. Some people don't trust mail-in voting in general, others don't have permanent addresses to receive ballots, others may not trust the post-office to deliver their ballot on time (this was a major issue last election), and others may not have received a ballot in the mail because they just moved or because of post-office error. Many people used the 24 hour in-person voting option last election in Texas https://www.nytimes.com/2020/11/01/us/texas-overnight-voting-polls.html