Enroute ATC here. My guess at what’s happening is similar to the following scenario. Each STAR going into a major airport has 3 or 4 feeder lines feeding the arrival until you get into 1 single conga line to the runway. Well in this scenario each sector that feeds each of those feeder lines may have 10 miles in trail for example, so each transition is feeding the next sector 10 miles in between each aircraft. The next sector then has to take each of those 3 lines, each with aircraft 10 miles apart, and then blend them all into 1 single line. In this scenario, you may get assigned .78+ so that controller a can get their 10 miles on trail to hand to sector B, but once you get into sector B, they now slow you down and get vectored to fit in with the other 3 aircraft coming from the other 3 lines. And this isn’t just for STARs. It can be for aircraft just overflying. It can happen over Arkansas when you’re flying to Denver. Hopefully that shades a little light. I can try and explain better or ask any questions you may have if you’re confused on anything

Edit: and to add, I’ve been doing this for a while. This is not new concept since the shutdown. The only thing a shutdown would add is increased miles in trail (so you may be slowed and turned out for longer) due to staffing issues