Many reasons
1) They have enough to do and learn in residency without having to learn someone else's job. They won't even spend time learning management of basic things for their patients like bp or diabetes control. These are guys with 250s, 260s and were rockstars in medical school
2) Surgeons don't get paid a separate fee for blocks. Payers consider pain control as part of surgical fee for a procedure. Whether they do local infiltration with a needle at the site or pick up an ultrasound, they get paid the same. So why bother? The supplies and the ultrasound cost money and it's a lot quicker for them to just place some lido with epi at the site.
3) Blocks take 3 minutes because we as anesthesiologists are good at them. We do a lot, we know the anatomy well and use needles and ultrasounds routinely. But watch someone doing them for the first time. In residency, our ortho residents didn't want us to place blocks because some of our attendings would spend half an hour going up and down the leg with the ultrasound "to really get a good sense of the anatomy". Then the ortho residents will take 5 hours to do a case that should take 45 minutes. I get it, they are learning too but serious double standard.
4) We do our blocks well. They generally provide good pain relief for the patient and there is a lower infection risk as we place the local under sterile conditions away from the surgical site. Same reason why we do the lines instead of the surgeons even though they are completely capable of placing a cvl.