Lucrative is relative. Yes, COBOL programmers are in demand right now, because most of them have retired. Does that mean somebody just starting out should expend the resources and time to learn COBOL? Probably not, because the return on their personal investment would be less than if they spent it on more current/in-demand technologies. OTOH, a programmer that already has COBOL experience, can still find employment.
It's like buggy whips. As the buggy was replaced by the automobile, the demand for buggy whips declined. However, until horse buggies were completely gone, there was still a demand, albeit smaller than in its heyday, for buggy whips. If you were an experienced buggy whip maker, you could still find employment making buggy whips. However, it would not have been a field for a new apprentice to enter.
Likewise with COBOL and the other languages mentioned. There is still demand for programmers with that knowledge, but it isn't a growing field. At some point the cost to maintain the code will become higher than converting the code because the cost of COBOL programmers will be too great given the supply and demand curve. For those who currently are COBOL programmers, that bodes well, but not for somebody just entering software development.
BTW, I use COBOL in the above languages, but the statements apply to most long lasting programming languages, not just COBOL.