I can think of other reasons why Hoyle might be denied a Nobel.
Firstly, he had been involved in some serious academic squabbles. Including one over the award of a Nobel prize (in 1974, but something not likely to endear him to the Nobel committee)
Secondly his first attempt on abiogenesis in space (popularised in
Lifecloud) had suffered severe (and apparently justified criticism) for (very) poor science. That was in 1978. So it was not just advocating panspermia, but publishing poor science in an attempt to support it that has to be taken into account.
So he had a very mixed record, and had likely acquired a lot of enemies - quite possibly including some of the people responsible for awarding the Nobel - by 1983.