The reason why it grew soooo much was the pandemic. During the early days of pandemic people wanted to get out of crypto and they still didn't wanted to take all their cash out to their bank accounts, that wasn't something ideal for them, so what they ended up doing was move their money from crypto to usdt
Fair enough I get your point about people wanting to exit crypto and into dollars( tether in this case since it's relatively easier) at a time of volatility due the pandemic.
so what they ended up doing was move their money from crypto to usdt which made it a bit more difficult because there wasn't enough usdt, there was only 4.6 billion and honestly crypto market is so much bigger, they were a bit late but not too late and increased it to 11 billion dollars, which people just bought it all because most still wanted out.
Just think about exactly it is that you have said here people have sold their crypto into tether but there wasn't enough tether to go around. ( the natural thing to happen in this case would have been for the peg to be broken I.e 1 tether would be worth more than 1 dollar)
However what you have said implies that more tether has been consequently printed to meet their demand. However instead of being bought by real dollars this has been bought and therefore backed using BTC or some other crypto.
Since no new dollars have actually gone into the system this would then again play into the argument that tether is not backed by dollars but collatrialized by bitcoin or other cryptocurrencies which would be truly alarming.
This of course assumes that the exchanges on which BTC has been traded for tether have not sent the corresponding real dollars to the tether corporation. ( And I really don't think even the big exchanges combined have 6-8 billion in liquid dollars lying around to send to tether )