Mourn not. These were purpose-built structures erected in record time to support a single program (and pressed into service for Shuttle & friends). They were first so they were by definition pioneering, but we've learned a lot since then.

The sad part isn't that they're gone. The sad part is that we didn't make them obsolete until just recently.

on one hand, "ha-ha artemis was made to reuse shuttle program and now look at this"

on the other... judging by the pictures nobody did the maintenance anyway, so it's straight up safety precaution and hazard removal

In a steady state economy the metal going into infrastructure is balanced by metal recovered from obsolete infrastructure. Demolition and recycling is part of the economic lifecycle.

Almost 70% of US steel production is from recycled metal. Structural steel is recycled at a 98% rate.

As your mourn, remember that this space can now be used for something else. It is easy to see what we lost, but it is hard to see what we lose by not getting rid of something obsolete.

These structures were not something we could reasonably make into a museum (too much work required to make them safe/useful for that, and there already is a nice museum in the city that I strongly recommend you visit instead), so it is time to move on.