Laser links would make everything more complicated and expensive. Radio antennas can share the same hardware to link with many terminals, not so with laser systems. They are point to point, so you need many more. They also require precise pointing, you can forget passive spacecraft. The number of 42 PB per day is about three orders of magnitude lower than the data rates required by SKA Low.

>I don't see why couldn't put that in space, today.

Because the electronics are not built for space. Space rated electronics is about a decade behind their ground based siblings. Radiation is one of the most problematic, degrading electronics and disrupting digital memory. You also need petabytes of temp storage. Which, again, doesn't exist. For reference, JWST carries a 70 GB solid state recorder, I think Roman has about 1 TB. Then there is all the cooling, which is difficult in space. Saying there are some start-up considering computing is not the same as it being possible to order a system like this today.

The question is not could it theoretically be done, but can it be done on even the sorts of budget of a space science mission. And the answer to that is no. SKA pushes computing and technology to the limit on the Earth, where these things are much more advanced.