this visa is only available to some of the brightest people in the world as it's limited to grads from only the top 50 universities. sorry, how do you not see the benefit of allowing these people to work in the UK? good for businesses, the economy, innovation and producing quality UK products. these grads are gonna come here and spend money on the UK and make the UK money in more ways than one.
long term these grads are going to have to switch to a regular work visa if they want to stay in the UK. the industries they work in will therefore be limited as well as the firms/companies/whatever in the industry because not every firm etc can sponsor someone - even the job roles are limited; in fact it's extremely limited when you compare it to where UK residents can work and what type of position they can work in. nobody can sponsor a visa for the office receptionist or paralegal even if they graduated from Harvard Law. hence, there's no way it will pose a threat to the average UK graduate; they likely are not applying for the same job.
also do you know the conditions an employer must meet in order to prove to the UK Home Office that it can sponsor someone for a work visa? one of them is they have to prove the candidate was a better choice, that they needed to hire this non UK citizen for this position and couldn't hire a UK grad. it ain't necessarily an easy argument to make.
it's also probable that the UK wanted to think of creative solutions to make up for the fact it won't see the same amount of workers coming into the UK now that we've brexited; nope, not nearly the same amount now that borders are closed.