The Ryzen 3 3300x is compatible with B450 motherboards. It’s the best choice for people who want to bring the best out of their Ryzen 3 3300x processors while keeping their budget on the low side. That’s pretty much the only reason why you should consider B450 motherboards, because on the flipside…
There’s no multi-GPU support, no fancy ports, not great for overclocking, and definitely no support for hardcore enthusiasts who want their PCs dressed to the nines with high-end hardware, overclocking, and multiple GPUs. It’s a huge tradeoff, but one that probably doesn’t matter to your average casual gamer.