Logistic Nightmares

It's not that you can't bring a beam weapon to another world, but you'll quickly run into problems maintaining it operational, because like our guns it's a finicky thing whose reliability suffers without proper maintenance.

Reliance on Divergent Physics

Something of a cop-out, but canonically at least some worlds in IW have different physical laws. Have it just so happen that many or most technologies above a desired level tend to be built using such world-specific physics, which means that they're likely to fail in other worlds.

Emphasise the Secret

Make it so that showing blatantly high-tech gear results in easily-identifiable rumours, which in turn results in powers that be bringing down the hammer. For a full brunt of the hammer, nudge the crossworld situation in a way that would make both Infinity and Centrum angry about such renegade forces and jointly act to thwart such unsubtle conquerors. Maybe broaden the phenomenon of destabilising Echos to non-Echo world types to justify that.