While that’s true for taxes alone, there are income gaps where a small increase of income can result in a loss of various benefits that were worth more than the increase. This can be things like food stamps, subsidized rent/childcare, etc… People end up stuck because while they could potentially earn significant advancement and increased wages over a 4-7 year period, they’d have to weather a significant deficit through intervening years.

Ideally there should be no cliffs, and all these social programs should have a sliding scale of benefits so a person can always benefit from increased income. Part of the problem is they’re managed across multiple levels of government that don’t always play well together, and a sliding scale might mean more benefits paid out to people that don’t currently qualify. That’s probably actually a good thing, but gets spun politically as undesirable.