You don't need to be able to "isolate" in the sense you mean to isolate in a way that is usable in biological experiments or to determine viral load.

There are two standards of isolation. There is the type you mean, where you have nothing but a large quantity of intact virions and no other biological matter (which is extremely difficult to do), and you have "isolated" in the cell fractionation sense (which is how all biology is done in a practical setting) where the cell fraction containing mostly virions and other organelles of similar size are contained. Within that cell fraction there will be some other biological material, but it will be sufficiently just viral bodies that it can be used for infection studies, or whole genome sequencing, etc.

There is nothing suspicious about this being the only standard of isolation that has been performed as it is how all biology is done. The standard you are talking about would be required to prove, beyond a shadow of a doubt, that what you have is what you say you have.

There is merit in demanding that standard under the suspicious circumstances surrounding this virus, but from a practical biology standpoint, that standard is ludicrous. The current standard of isolation being employed on the other hand gives a genome sequence with sufficiently high statistical accuracy and valid testable virions sufficient for most reasonable experiments. It also allows for reasonably accurate tests for viral load.