Earlier quoted context omitted.
Realistically I would say a lot of engineers are easy to fire. You only need a certain amount of engineers to do maintenance.
Engineers are easy to fire, but incredibly hard (and expensive) to hire, especially if you become known as the company that'll fire people immediately in a crisis. There's a fine line between saving money now and spending it later, and I'm sure Yelp - just like every other company out there - is trying to figure out where does that line lay.
The thing that truly influences "hard to hire" is supply and demand. With the influx of bootcamps Software engineering supply has increased and with COVID-19 decreasing demand Engineers may no longer have the luxury of picking and choosing like they used to.
I'm an engineer btw. Just viewing the situation from a realistic lens.