Some more responsible device manufacturers are doing this. For example, the industrial equipment I worked with charges batteries much more sustainably, also by charging it with less current.
Remember, there are multiple factors when it comes to batteries degrading. Voltage (how far the battery is charged) is one of them, but so is the charging current (how fast) and also the temperature during and outside of charging.
Personally, I usually use slower chargers for my laptops and phones to prolong the device lifetime.
I don't understand the obsession with fast charging. I can probably count the number of times I needed to charge my phone instantly on one hand. The other day I bought a MagSafe charger because my new phone doesn't fit properly on my old wireless charger, turns out it doesn't support the "legacy" 5W power bricks. Now it's sitting unused in the drawer because I don't want to charge with more than 5 watts.
Also an issue for travel-friendly charging solutions: there just aren't any truly lightweight USB-C cables that merely support the old USB2-era maximum currents that are perfectly fine for overnight charging. If you count grams, you're ent4irely better off with certain cable models of bulky A to micro-B + adapter.
And even voltage is just a rough proxy for the actual state of ions in the anode-cathode dance.
When voltage goes down with temperature, the charge state does not change. But drawing a certain amount of joules will be very different because at lower temperature you'll need more coulombs for the same amount of joules, aka VAh.
And at nontrivial discharge throughput, observed voltage will drop to much lower values than what a snapshot of the current ion-dance state would look like at steady state. This is the "smartphone SoC must not try performance bursts as it used to" scenario.
Remember, there are multiple factors when it comes to batteries degrading. Voltage (how far the battery is charged) is one of them, but so is the charging current (how fast) and also the temperature during and outside of charging.
Personally, I usually use slower chargers for my laptops and phones to prolong the device lifetime.