Dutchie here, same for me. In English it's easy to say 3pm or 9pm but in Dutch that would be 3 uur 's middags (in the afternoon) or 9 uur 's avonds (in the evening) so 15 uur and 21 uur is shorter to say. However, when it's "am" I always say 's nachts (at night) or 's ochtends (in the morning) to avoid confusion. But all digital clocks in NL are on 24h. I don't think I've seen anyone with a 12h notation on their phone or anything else. It's such a standard, I don't even think my oven and microwave have a 12h notation option.

I think it's just a case of uneducated ignorant Americans stuck in the past, while also having no clue there exists a rest of the world where people are not weird. Like with their imperial system and IALA buoys system (for the entire American continents by the way).