I view this generally:

Motivation to stay is being directly excited by the work you’re doing or the thing you’re building. You want to work where you are. If another opportunity comes along you probably wouldn’t consider it.

Resistance to leaving means you’re at a pleasant place to work, the money is good, and you like your job, but you’re not super excited about the thing you’re building. If another opportunity came along you might jump if it’s something you really want to do (this is harder if your current pay is high and job is pleasant).

I think they are referring to Herzberg? https://en.m.wikipedia.org/wiki/Two-factor_theory

Sounds like a different way to express that.

Think about someone who works at an non-profit NGO versus someone who works an 80 hour week at an investment bank. The NGO worker might only be making $30k/year but he stays because he really cares about his work. The investment banker might hate his job and hate the long hours but stay because of the high salary he'd be unlikely to match elsewhere. The NGO worker has high motivation and low reluctance, the i-banker has the opposite.

The actual technical term for this is motivation vs. hygiene: https://en.wikipedia.org/wiki/Two-factor_theory

The way I think about it is motivation relates to the things you actively enjoy about your job. These are the "here are the neat things I do at my work" type of items.

Reluctance to leave is the sum of things that make you want to stay where you currently when someone else tells you about all the exciting things they do at their work. It's more like friction keeping you where you are.

I think motivation to stay is the positive. Like you genuinely like going to your job.

Reluctance to leave is that even if you don't like your job, leaving is even more painful, maybe due to the loss of salary, or because the interview process is too much of a hassle, or other opportunities are just as bad if not worse, etc.

I think that should have been “motivation to work.”

If I had to guess, differing incentives. Both are synonymous for "why they stay" but with different base reasons.