I realize that. But the group in question is composed of six newbies. They still don't always successfully track their resources within a session; I have no faith that they'll track them beyond the session. Think me lazy if you wish, but I have no interest in doing all the work of tracking from week to week.
I like Popcorn initiative, but not in 5e. As part of keeping things streamlined, they went for the shorthand of a lot of spells and features lasting until the start of your next action, or otherwise using your action as a shorthand for "everyone has gone once". When the initiative changes round to round, sometimes effects will end up doubling up when someone goes slow one round than fast in another, or not affecting someone at all in the reverse.
With a player chose initiative system they can really take advantage of this. "Oh look, foe X cast Shield during my action, but since they haven't gone yet this round I'm going to give them initiative next so the AC bonus is gone before my friends attack him." And it's not even good for the goose, good for the gander because a DM who purposefully trying to mess over player features so they are of minimal use is not fun to play with.
Yeah, I agree there are some unintended action economy consequences in 5e when you shuffle up the order round to round. That said, a bad DM will find other ways to be bad - for the sake of discussion, I assume players and DMs are upholding the social contract to play in good faith.
In any case, we tried popcorn initiative for a couple of sessions in two 5e groups and both groups generally agreed it was too “gamely” for their tastes. It’s interesting the Angry states he doesn’t use it either.
As [MENTION=6788736]Flamestrike[/MENTION] mentioned, D&D mechanically is about resource management. If you have players that aren't interested in resource management, and as newbies not yet invested in 5e, perhaps the right solution is to look for another game system that better supports your table's play style. I love 5e, but it's not the only good fantasy RPG out there, and there are many that have minimal resource focus outside of the scope a scene.
"I don't like D&D being a resource-management game. How can I make D&D be not about managing resources?"
'Play a different game'
DnD is all about resources (mechanically). That's why things like the DM policing the adventuring day is vital to encounter and class balance.
If those things are not balancing, you're not managing the adventuring day, or doing your job as DM.
I shudder each time I see a DM ramping up encounter difficulty in response to nova tactics or the 5MWD.
That just makes things worse.
Game still works fine. There’s just less balance between classes. That’s something I don’t prefer but it may be a better alternative than trying to change the whole style and adventure pacing to shoehorn 6-8 encounters per day just for the sake of class balance.
the classes hurt the worst by a short adventuring day are also the easiest to fix with magic items that the casters won’t be very interested in
Personally, I find that you can fairly easily maintain balance by simply putting in a bit of variety. Even if you mostly use short, difficult adventuring days, as long as you throw in a handful of longer days in the campaign the players will be far more judicious with their resources and less likely to nova. As long as you avoid nova, you can have short days without unbalancing the classes. The long rest classes essentially become more of a safety valve, since if they're severely pressured by an encounter they can nova in order to prevent a TPK. But it won't be their go to move, since they'll always be wondering if today is going to be a long day. IME, anyway.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.