I believe this is the main reason. Since they can store their coins in exchanges or online wallets for free, hardware wallets stay in second plan, because they are expensive, especially for small investors. If they have 200$-300$, it's likely they will prefer to use this money to acquire more btcs, instead of purchasing a wallet.

In my case, I spent about 150$ in an more archaic model (Trezor One) years ago, but I just did that after several years of personal bitcoin adoption. Anyway, if I was going to purchase the modern hardware wallets' models I would have spent much more.

But I don't think it's hard to setup and use hardware wallet. Anyone who is able to use an online wallet or exchange won't have any difficult at a hardware one. There are so many tutorials, guides and videos disponible that the whole process becomes pretty simple.