There was an interesting comment on this in a recent government finance report. An owner of a company said, "I'm having trouble filling all my open roles". When asked, "Why not offer more money?", they said, "Because then I'd have to pay all my existing workers more too and I can't afford that. It's cheaper to just pay them all overtime".

So this could explain why they won't just pay more -- because some people are already willing to do the work at the current pay, and it's cheaper to have them work more.