Because near/mid infrared has many uses other than high-z objects, and it’s been something of a relative blind spot to us until now, although before Webb we did have Spitzer.

For far IR/submillimeter observations we had Herschel in space, SOFIA in the stratosphere (flying on a 747), and several large terrestrial telescopes at very high altitudes can also observe at FIR/submm wavelengths. But sure, there are likely many astronomers who would love nothing more than a new spaceborne FIR telescope, given that it’s been more than a decade since Herschel’s end of mission, and SOFIA was also retired in 2022.

For microwave we’ve had several space telescopes (COBE, then WMAP, then Planck), mainly designed to map the cosmic microwave background. That’s the farthest and reddest that you can see in any EM band, 300,000 years after the big bang.

Past microwave, that’s the domain of radio astronomy, with entirely different technology needed. We have huge radio telescope arrays on the ground – the atmosphere is fairly transparent to radio so there’s no pressing reason to launch radio telescopes to space, and their size would make it completely infeasible anyway, at least until some novel low-mass, self-unfolding antenna technology.

The lower the frequency, the larger the wavelength and thus the larger the cupola needed to detect it. That's why radiotelescopes are on earth, they are HUGE.

Excellent question!

The longest wavelengths of light are generally classified as "radio".

So radio telescopes have been tasked to explore the very early universe.

https://en.wikipedia.org/wiki/Reionization

If I understand it correctly, the "Period of Reionization" is first light we can see from processes like stars and galaxies.

There was ionized plasma at the beginning but the universe was like a really thick fog everywhere, and that first light was scattered around and you can't really see stars. As the universe expanded, that fog cooled down, and you could see, but cold matter doesn't emit much light, so there wasn't much to see. It took a while for gas clouds to collapse into the first stars, heating up the gas to ionized plasma once again, so it's re-ionized matter.

The Low Frequency Array, LOFAR, has been used to study this "Cosmic Dawn".

The Square Kilometer Array was designed to explore this era.

But! Not a radio telescope JWST has revealed unexpected, huge globs that seem to be galaxy-sized gas clouds collapsing into (maybe) black hole cores; the thermal emission from the collapse isn't nuclear fusion, so I don't know if those are "stars". But it's very early light.

Honestly, every time a new class of telescope is built, it discovers fundamentally new phenomena.

https://duckduckgo.com/?q=LOFAR+square+kilometer+array+reion...

https://news.ycombinator.com/item?id=44739618

https://news.ycombinator.com/item?id=46938217

I searched "Reionization" and "Cosmic Dawn" plus some favorite telescopes via web and here using the Hacker News search (Agolia).

(Certainly you know the difference between radio and infrared, but I had to look into how those choices of telescope have observed different aspects of Reionization Era, got nerd-sniped, and just had to write it down in a couple of sentences.)

It's safe to say that if we are sticking a 6-ton 20ft mirror into space that the scientists probably have a reason for it...

Lower frequencies are microwaves and radio waves. We already have the square kilometer array.

"just an infrared telescope"

how about you go make yourself conversant with "just" the technical requirements of the main cryogenic pump onboard, leaving out the rest of the thermal management systems for whatever remains of your life, which will have to be long in order to fail honorably.