In addition to the 1000 hour 121 time requirement any of the airlines you could name in the USA have a strict seniority system. EVERYTHING is based on date of hire. Choice of type, schedule, rate of pay, vacation, everything. When you get hired you are the bottom of the list so you get what no one else wants. The 1000 hours is not a problem at the major airlines because you will sit right seat for a few years. I did hear Delta was close to a one year upgrade for New York based MD-80 Captains a while back but that's not normal. Probably because no one wanted to sit reserve in NY. Some of the regional airlines are having the opposite problem. They are bleeding Captains to the majors so fast that their upgrade is less than a year and they have pilots who could hold the upgrade by seniority but don't have the time. So a pilot junior to them on the seniority list is upgraded. However that pilot is stuck at the bottom of the Captains list longer because when the first pilot finally gets their 1000 hours PIC and upgrades they move back ahead of them on the Captains list.
The 1000 hour 121 time requirement is fallout from a crash in 2009. While both pilots had more than 1500 hours TT there were several changes made to ATP training requirements and airline operations.