He's got some weird expectations there. Retail often limits people from going full time so that they don't have to offer them a larger benefits package or things like that. They'll regularly have a group of employees that nearly work 'full time', but do not consistently qualify, specifically to avoid that label. They probably wouldn't offer it to her regardless. Not that she's a gold star employee to begin with - her supposed attraction to a human parasite with no work ethic strongly suggests she doesn't value 'hard work' either.
That said, just imagine the larger implications of this statement. He wants Kat to take on a full time retail job (soul sucking), in the middle of a pandemic where retail employees are not in a great position to begin with, while he literally makes $120k per year... and burns it on nothing. I'm sure a similar situation was not at all a contributing factor to Leanna's departure.
And on top of that, you aren't supposed to mention Kat as a second income in the context of his begging. That's been verbotin since he was playing her up as a second income when he was begging for her moving expenses. Weird that it has suddenly come up again, now that there are serious questions surrounding his finances.