The original value propitiation of tether was... "A one to one, 100% reserved USD backed cryptocurrency that you can buy/sell any time directly from them"
They originally promised a website where you could buy/sell tethers directly for 1 USD. This is different from all the other stable type coins that achieve their pegs using various chain and exchange strategies. Tethers proposition was to maintain it's peg to USD by literally holding the cash and being the primary point of purchase/sale. Not investing it. Not operating fractional reserve. And not buying/selling with a spread. Every profit making strategy goes against their original proposition.
The reason this was the proposition was to supposedly make it easier for crypto traders. At the time everyone was having problems cashing out their cryoto. Tether was basically promising that they could fix the USD exchange problem by holding all the cash and not being an exchange.
Now they never actually delivered any of that. The website never reliably appeared and now tethers are traded on an exchange like any other crypto coin. And I suspect they did actually make a stack of profit by printing tether and selling them on exchanges. But that makes it a scam because they weren't following their own rules that they laid down at the start.