Why? If you don't get give out enough items, then what's the point of attunement? My 12th level party is now at the point where they have to make some really hard choices about what items to use, which makes giving out items even less of a problem for the power curve.Magic items are fun, but they accumulate. So you need to periodically thin the accumulation.
The problem with attunement without slots is that you can objectively pick the three best items & the gm can no longer have a powerful thing that conflicts with some other powerful thing so only one can be used. Now you unattune the weakest thing & attune to both powerful thingsI haven't had a problem with it. Moderation in how many magic items are given out in the game prevents it from being an issue. There's no need for everyone to have six magic items by 5th level like in the last couple of editions.
Deciding what the best items for you are can be pretty subjective.The problem with attunement without slots is that you can objectively pick the three best items & the gm can no longer have a powerful thing that conflicts with some other powerful thing so only one can be used. Now you unattune the weakest thing & attune to both powerful things
can be yes, but the old system allowed mistakes to be corrected. Lets say Alice gives her party two magical widgets that seems nice but innocuous. Unfortunately she did not consider how the first will be when bob gets another couple levels & the magic item becomes much more powerful thanks to some extra class features. The second she thought would be a good "oh crap just hit the fan" button they eventually use up, but didn't consider the possibility that it would get used regularly and never go away because the party never uses the last charge.Deciding what the best items for you are can be pretty subjective.
Magic items are fun, but they accumulate. So you need to periodically thin the accumulation.

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