If you're saving large amounts, does it go in a brokerage account?

So I max out my 401 and have the match. Then I invest either 3.5 or 4k a month in my brokerage account in etfs, I haven't done a backdoor Roth because honestly it's such a small amount you can contribute from what I understand. Is there something I'm missing? People put huge amounts away must just put it in a brokerage right?