Silly prices and questionable quality.
I did buy a few space sets (Saturn V, ISS, Eagle moon lander and Shuttle) and the Shuttle was definitely at the far end of what I am willing to pay.
There’s the strange use of odd-coloured bricks where you don’t see them which always feels like they’re rooting around in the parts bin to get rid of earlier overproduction. They use decals far too often, even in really expensive sets. And apparently, there are sometimes issues with colour discrepancies where you do see them.
Their competitors come up with comparable and often better sets at lower prices, such as the COBI Concorde I bought a while ago.
And finally, some of their product decisions are just middle fingers to their long-time customers, like the revamped City sets that are incompatible with the series that they’ve been selling for decades.