Bonus actions are still needed. The reason yall can't see the issue is because 5e also has almost no bloat. You add bloat and more and newer interesting "bonus actions" and you make them all free and can use as many on your turn as you want as long as they have a different effect and you have a high probability of eventually having problems after enough bloat.
You don't need to worry about bonus action restrictions when there is no bloat though. A lot of problems kind of fix themselves when you eliminate the bloat But don't think for a second that such "unnecessary features" in a bloatless system wouldn't be the greatest thing ever in a bloat filled system.
Also a fair point. The more options included and the more 'min-maxy' players you have, the bigger issue stacking will be at your table. And if you have to make complex exceptions to curtail it, you will surely end up missing the simple bonus action. But, reading through the PHB, there's actually less bonus action features than I thought, which makes stacking them something you would actually have to work hard to do - and I'm not sure it would be worth the effort.