There's an extra 39,000 university places, so on the whole the government is increasing spending. For every degree that is made cheaper, the government needs to make up the difference and from what it seems, the aim is also to increase students studying certain degrees that have a higher probability of employment.
Actually, from a few things I've read this doesn't seem to be true: It's actually a cost-neutral project. To me, that feels more like a classic divide-and-rule strategy: make sure there are enough people who are better off under the new system to hide the fact that on average each student will have to pay more and the government less for the same degree.
From the discussion it seems like the rise in demand is Covid-19 driven. Not clear whether that means it's temporary or permanent, but particularly if it's temporary there isn't actually a need for it to be cost-neutral. In an attempt to help the economy recover from Covid-19 the government will be throwing money at various things they think will help the economy recover, and I don't see why education shouldn't be one of those things.
I'm a straight maths-science student, and I don't think I took a single humanities subject in university (despite them at the time being cheaper). Like other commenters, I think, while I knew the cost of my degree, it was unlikely to change me studying what I wanted to study. And, like Bri said, I always considered it reasonable that humanities subjects cost students less because they generally cost universities less to deliver.
I've probably heard all the critiques of Arts degrees and said some of them myself when younger. But if you look at my out-of-work hours reading and writing now, it's much more skewed to the humanities, because they're important. I hold a technical role, and my technical skills help, but so do my non-technical skills.
And this doesn't just affect students in Arts degrees (the soft targets the government think they can get away with). It affects maths-science students who want to take humanities subjects as electives - electives that could be more useful for making them a well-rounded student than taking another technical subject (like, um, I did...). To take just one example, I remember a time when we were being told we were in the Asian century and in a global economy, so students should be encouraged to take languages like Indonesian and Mandarin. I don't know how often that actually happened, but this would be a disincentive to it.
Finally, unless you think the number of people needed in these fields or with these skills is zero (and I don't) there is
possibly an argument to try and limit the
number of students supported by the government - but I don't see the argument for keeping the same number of students (or possibly a little lower) and supporting each student with less government money. If you want to get the best return on government money then you want to try and get the best possible students for each area - and that applies for
both the humanities and the sciences.