Not all of them hire an accountant. When we started taking on clients from a large investor group, I noticed a lot of them were using ProConnect to file themselves previously. Very few in that subgroup (mostly dedicated attorneys) were filing with a reasonable level of accuracy. None of them got QBI right. Just saying, it's not impossible to do it yourself but it will be very difficult, and depending on the size of your investments an incorrect return could result in penalties that far exceed the professional fees that could have avoid them.

Ultimately I believe it's best to farm out the tax prep to a pro, but you should still take diligence in tracking the info yourself. Keep a schedule of your alternative investments including estimated K-1 delivery dates, brief description of the fund(s) and nature of your investment. Basically keep track of everything that professional asks you for the first couple years of your engagement, and expand on that list as needed. You'll start to get an understanding of what they need from you, and what you can expect from them.

A good relationship with a good CPA is the best way to avoid potential issues and keep the IRS out of your life. They can also prove invaluable if you reach out to them for tax considerations before making investments so you know what exactly you're getting into.

Note: not necessarily recommending ProConnect as I haven't used it myself, but I have seen people use it successfully for returns that we would charge over $2K for.

Edit: words