There are high salary requirements for ILR as a Tier 2 that need to be met.
That's the problem for quite a few, and always has been for those who entered on other now closed visas too: they don't earn enough to renew their visa or apply for ILR and they can't find an employer who will sponsor them on that higher wage.
For the Tier 2 General visa, I
think the renewal will need to be for a higher salary? Those doing a job on the UK's SOL (Shortage Occupation List) don't need to meet the higher earning requirement that others must do and I
think that is the same for those doing some types of PhD jobs even if they don't have a PhD, because it is the job that counts as the skill wanted.
If they don't meet the financial requirement to renew their work visa or for ILR, and they want to stay, they have to look for another route to settlement, often that's a partner of/marry, a British citizen as that financial requirement is much lower