We use Intel Compiler mainly on supercomputers with Intel CPUs. IT can produce faster code. However it is not great to work with it. It lacks features of the newer standard and it is really slow. Usually we develop with clang or GCC and then we go on the cluster.

I am sure that plenty of existing HPC cluster will remain intel, the interesting question is how much of the new HPC computers will be AMD.

or is there any HPC specific reason why Intel would still be preferred?

Several new HPCs are already using AMD [1] and that trend will probably continue if AMD continues to put out competitive products.

[1] See the Top 500 list that, by my count, has 26 of the top 100 HPC systems using AMD EPYC CPUs as of their June 2021 listing https://www.top500.org/lists/top500/list/2021/06/

Existing install base most likely. It's not as if HPC clusters get replaced every other year. Even upgrades usually stay with the same platform and don't switch from Intel to AMD or ARM-based systems.

Yes, this is the only place I see alternative compilers used much. We have Intel and Nvidia compilers available to our users.