What is the downside of using WordPress?

WordPress has real downsides: plugin maintenance, security patching, and update management all fall on you or whoever manages the site. Left unmaintained, outdated plugins are one of the most common ways a WordPress site gets hacked.

It also has a learning curve if you're managing it yourself, and a poorly built WordPress site (bloated themes, too many plugins) can run slower than simpler builder platforms. None of this is a reason to avoid it, but it does mean someone needs to own the upkeep.