I picked the second example exactly to elicit a response such as yours. It's ultimately a word from a foreign language. At some point it got used by English-sp

I picked the second example exactly to elicit a response such as yours. It's ultimately a word from a foreign language. At some point it got used by English-speakers and then it spread and got used more and more. Lots of foreign words get used. Some catch on and some don't. That's just how language evolves. Pajamas is just an example of a foreign word in a late stage of this evolution