LibreOffice is good for a lot of tasks but it's bloated, and takes time to start up. Wordpad is great for all sorts of quick tasks when you just need to edit a quick RTF like a poster or some basic letter, and don't want to stare at a ribbon full of functions you'll never use.
LO for Windows launches with a launcher that pre-loads it a boot time. I find Writer to be pretty pleasantly light-weight on a modern computer. A lot of its performance shortcomings are a bit exaggerated especially on modern equipment.
Pre-loading at boot time is a tradeoff, and it'd be nicer not to have to pay it.
Cold load times aren't terrible on modern systems, but wordpad is much faster. (Microsoft Office isn't great at fast loading either).
LibreOffice doesn't come preinstalled with Windows. It also is very bloated compared to WordPad.