I skimmed https://wikipedia.org/wiki/Decimal_separator but still don't understand. Why does this difference exist? Also, why did the conflict eventually settle into something between full stops and commas? What stopped other symbols from continued usage like bars or underscores?

It seems weird that a system would eventually settle on just full stops and commas, yet not settle on where to put them. If your system is going to converge strongly on two symbols, finish the job!

> Why does this difference exist?

Same reason why there are different date formats, weeks start on Sundays/Mondays (or Saturdays), long/short scale numbers, drives on left/right, different wall sockets and plugs, different train gauges, and of course metric/imperial.

It's a mix of tradition, conventions, inertia.

Because in English you say "three dot two", whereas in German it is "Drei-Komma-Zwei".

It just reflects the spoken language. And having the unused symbol then be the thousand separator is natural.

Interesting, I did not know this, but a little bit doubtful. Wouldn't it be the other way around? Explicit spoken language coming from being written that way.

Maybe at some point originally, but now you can't change it. Spoken language resists attempts to shape it by committee, and written language has to begrudgingly follow its lead.

Not in e.g. UK.

The UK is sadly not in the European Union and it wasn't included in this study.

Just responding to comment about European countries using decimal separator.