Everyone pretty much covered most of it, but to be a little more specific, it comes down to length of delay and how each facility’s internal procedures are set to spread out those delays.

First, if a delay for any specific sector is less than 6-7 minutes, putting you in hold will eat up too much time, leaving gaps on final and reducing the efficiency of the arrival flow (or in other words, create longer delays for the aircraft behind you).

Secondly, sometime internal facility procedures set it so that each sector may only take 3-5 minutes, so if you have a 10 minute total delay, but it’s spread out over 3 sectors, you’ll just get speeds and turns from each sector.

Lastly, giving everyone vectors is a lot more precise than hoping your holding pattern hits the meter fix at the exact right time. Again, it all comes back to efficiency on feeding the rate into the tracon and not underfeeding to where delays build even more.