Depends on the show. A lot of concerts block some seats for the stage design, which allows you to reduce seat totals. Kendrick and most arena tours do this.
For instance, Taylor at Arrowhead Stadium:
Her stage basically cuts off an entire eastern corner of the stadium, plus some of the middle. Arrowhead has nearly 80k capacity and she sold 55k tickets.
Essentially, 30% of the capacity was taken up by the stage (and other areas that are blocked). Could Taylor have sold it out with a smaller stage? Of course. She could probably sell out every ticket in a 100k capacity stadium. Back to hip hop though...SoFi has an official capacity of 70k (it can be extended to 100k for special events). If Travis, Kendrick, etc had a stage design similar to Taylor's taking up 30% of capacity, that leaves you with about 49k total available seats. Which is what Kendrick did in three Crypto Arena stops last year, as you pointed out.
This is why I'm shaking my head at some of the arguments in here about Jay. You don't think 50k people would show up for a Hov show in a major urban city like LA? The reason big rappers don't do stadiums has less to do with selling them out and more to do with the costs/time involved. Why do SoFi when you can do Crypto three nights in a row like Kendrick. Or like Drake did Kia Forum four times, plus Crypto two times.