This is probably a politically fuelled ruling. Boris Johnson wants to 'appeal to the masses' by making high-visibility rules like these, which sound good on paper but probably do more harm than good.
For a small example, there was a recent case where an MP of the governing party (Charlie Elphicke) was convicted of sexual assault. As part of the sentencing process, defendants can submit character references ("He's a hugely charitable, reliable, all round good person and this offence is entirely out of character", that kind of thing) and several Conservative MPs sent them on his behalf, but asked for them to be kept confidential (presumably to avoid political damage at the upcoming election).
The judiciary were having none of it. The trial judge released the letters anyway, and the Lord Chief Justice (head of the criminal courts) rebuked the MPs for trying to influence the decision of a judge.[0] And this for something (character references) which are pretty mundane.
They really do not like bowing to political whims.
[0]: https://www.doughtystreet.co.uk/news/character-references-cr...
The UK government has been on something of an anti-judicial kick for the last year or so since the decision in Miller II/Cherry, the prorogations case (and a few other cases that haven't had as much press attention such as the Privacy International case on ouster clauses).
They've been talking about "reforming" or "scaling back" the Supreme Court—perhaps simply by renaming it—and talking about how judges have too much power, and are too "political", which somehow they propose to fix by replacing the independent appointment process with a more explicitly political one.
Also, if Johnson and the Conservatives wished to bring about the same result, they don't need a Supreme Court decision to do so—they have an 80 seat majority, a large chunk of which come from disaffected Labour voters in the so-called "Northern heartlands" who are perfectly happy to have employment rights improved. The Conservatives could, if they wished, quite easily pass primary legislation to specifically make gig economy or app-based workers have the status of workers under employment law - they'd probably get cross-party support for it.
See:
https://www.theguardian.com/law/2020/nov/15/supreme-court-pl...
https://www.lawgazette.co.uk/law/government-urged-to-rename-...