Hi, yes, this a good sub for questions on historical linguistics (see also /r/linguistics). There's always room for more input on this topic, but while you're waiting for more answers, you can check these out for previous responses

• During what period of time did the informal you form, of 'thou' start to and finally become archaic in English? - featuring /u/gingerkid1234

• How did the English informal pronouns ("thou/thee/thy"...) become defunct? - featuring /u/lngwstksgk

The answers above provide a lot of insight. I'll add one other factor. Having separate formal and informal forms places a lot of burden on a speaker. If I address someone outside my family and closest friends, how do I know if they are informal to me or not?

Look at the context in England in the 1600s. There was a revolution. A king was executed. Parliament asserted authority at the expense of hereditary nobles. A middle class was rising. The sharp distinctions of social hierarchy were being disturbed. Against this background, it may just have been easier to call everyone "you" rather than navigate the complexities of doing otherwise.