> Why are different frequencies used for APRS in Europe and North America?
You wouldn't believe how incredibly hard it was to get a single frequency for APRS just in North America!
APRS came late to the 2 meter party, the bandplan never anticipated there may someday be a system that could benefit from a single nationwide frequency. Use of the band was coordinated locally and therefore had no single open frequency that could be used everywhere in the US. In the early days APRS activity was on 145.79 (generally designated an experimental freq, APRS was experimental then) and 145.01 (a digital freq often coordinated for packet nodes and BBS) in the US along with a few local areas using other frequencies. Most of Canada used 144.39. A proposal was made by the Shuttle Amateur radio Experiment (SAREX) in the late 1990s to move APRS to 144.39 in the US so the soon-to-be-built ISS could use 145.800 worldwide (it was useless over US due to QRM from 145.79).
A huge amount of angst followed, including some prominent APRS leaders arguing that SAREX promises of APRS on the ISS were a lie to grab our freq, and a nationwide donation fund for crystals, duplexers, and other hardware changes needed for the new freq.
Before the new millennium began APRS was on a single North American freq, making it better than before. SAREX, now ARISS, has certainly delivered on it promises. The doom predicted by weak signal operators at the low end of 2 meters never materialized. The great APRS QSY turned out to be one of those rare things in ham radio that worked out for everyone.
I can't imagine that ever happening on a worldwide basis, where either North America or Europe initiates a QSY to accommodate the rare trans-atlantic balloon flight!