When you're talking about software you're talking about issuing a series of commands that execute in certain ways that produce a desired result. While you may have threading to give the appearance of concurrency(or actual discrete cores/etc) it's still largely a serial operation(with pipelining under the hood but largely not exposed at a software level).
In contrast FPGAs, CPLDs and the like use as you said Hardware Description Languages. These languages are not about issuing a series of actions but instead describing a blueprint for construction of physical hardware units(via SRAM LUTs, ASIC lithography or the like). Many things that are common and expected as a part of software(looping, blocking, etc) are either anti-patterns to not available at all.
Asking someone who's familiar with software to write HDL is like asking a Civil Engineer to do the job of a Mechanical Engineer in designing the drivetrain of a car. Both are professional engineers but they have vastly different skills.
I've spent a fair time in both worlds(although more on the software side) and learning FPGAs was like hitting a brick wall for ~3 months until you realize you have to unlearn all you know about software and build up an understanding from the hardware side first. It's also probably why firmware engineers tend to write so much copy/paste code and software engineers tend to write code that uses an order of magnitude more resources than they actually need.