If there is an increase in the demand of stablecoins like USDT it means the price of Bitcoin will also be increasing? Upon what bases are you putting forward this claim? Do you even have any?
There is a very young FUD that started back in 2017 where people say bitcoin price has been rising only because they print USDT and pump it into bitcoin. That means a lot of newbies believe in such FUDs and think there is some reality there. The fact is that stablecoins in general are mainly used in pump and dumping altcoins and by traders who want to escape the volatility of altcoin market during bitcoin rises when they dump hard. There is also a niche market for those who want to transfer funds between exchanges which is where stable coins come in again.
Most of the times bitcoin/tether volume is less than 10% of the total volume.