了 as le or liǎo, too.

Did it get more numerous with the adoption of simplified characters?

I'm not sure, but I believe that most, if not all, mergers from simplification were homophones.

Yes, it did if you're not a mandarin speaker. The simplification process was biased towards Mandarin and there are some words that were merged that have different pronunciations in Cantonese but not in Mandarin.