Ya, there is a huge upfront cost to building a rig (engineering hours alone are insane lol) Especially offshore rigs. Also, building a new rigs takes a long time, like several years, and these contractors want to churn out profits ASAP.

Also, most rigs are mobile. Once they are built, they can be moved to new wells. The ones that are not mobile are left there, and when new tech comes out to suck more oil out of a well, they are updated and reused.