There are many reasons and it is not so much opposed to him just because but the party Libertarianism that he more or less represents.
The isolationist aspect of it is not remotely realistic for starters.
Rep Pauls assertion that we are the root cause of 9/11 is not going to endear him to many conservatives either.
I am sure there are folks here that can give a far more detailed answer and encourage it.
Lets keep in mind that what appears was a curious question was civially asked and answer it civially likewise.
This entire forum Bertram was founded as an offshoot of another one that was "invaded" by Paul supporters.
This part is opinion but given the failings of that political idelogy to stand the test of debate they resort to a lot of table pounding and asserting all who don`t follow them are not true conservatives.
An admin over there became part of that and demanded they be bowed to and began wantonly banning any that disagreed.
It is a sore spot to this day,and will stir passions regarding the subject,just so you are aware of that.