I guess after Bitcoin reached its first ATH in 2017, some mainstream Media started referring to ALTs like XRP and ETH by the abbreviation of crypto. I started hearing crypto from that time, though I may be wrong this is my opinion.
Plus it is easy to write crypto than cryptocurrency and also it is easy to pronounce.
I have come to the conclusion that the term "crypto" came about because people wanted to use a more attractive name than "altcoins." The maxi in me will continue calling all "cryptos" altcoins! I will call coins I respect by their actual name, but as a group they're always altcoins.
Altcoins isn't a bad word anyway and they didn't came up with a word like that for no reason but before they went there, it all started first with the word alternative coins. Any coins next to btc is alternative to btc or altcoins for short. Calling all cryptos an altcoin/s can be wrong imo, because bitcoin is included there and btc is the main coin (not an alternative) but I have no issue when you only say "coins" because a coin can either be an altcoin or a bitcoin. I agree with pakhit. It was in 2017 where the first massive ath came in. This then makes cryptocurrency became popular. Being lazy is normal to humans. This makes them shortcut things especially when writing.