Let us say, Thailand joins QUAD, it will not lose its sovereignty because the USA or India has no reason to move its troops through that country. It is far away.
Now, look at the map of Bangladesh. In the 1st look, you will see that BD is surrounded by Indian land. But, in reality, BD land hinders IA troops to move to its NE.
So, in times of war, the IA troops garrisoned in its NE all become worthless because they do not get supplies from the Indian mainland. India cannot go to NE via its Siliguri fast enough to contest PLA entry.
In such a scenario, it loses its fight against China in Arunachal and ultimately NE is lost. This is the reason BD is most important for India and QUAD.
When BD joins QUAD, there is no doubt America will force BD to allow IA and Bd troops to conduct multi-division troop movement exercises inside BD to prepare for a real war. And in a real war, IA troops use BD land and by QUAD TREATY, BA cannot contest this entry and movement.
When this happens, it will be the starting of losing the BD sovereignty. Note that China will no more support BD in its friction with India because BD has betrayed China.
BD enters the greedy mouth of the Indian dragon.
