The question is similar to…
Why don’t we have pocket devices that can absorb pollution from the air around us?
Why don’t we have a device that we can sync with our brain to feed new thoughts and control the existing ones?
Why don't we have flying cars already? (Those in the 1980s really thought we would have such cars by now!)
(Courtesy: Trusted Reviews)
Not that these won’t happen. It just takes time.
Such massive developments and innovations take a lot of time. Remember, we've had smartphones for only a slight over a decade. Consumer internet is only 2 decades old.
Until a few years back, the idea of "fast charging" was still a dream in the Smartphone segment.
So, if we don’t have devices that charge our phones instantly, it's because such innovations take time. They don’t happen in an event. They happen out of a process.
Also, not to forget, having such devices have certain limits at present.
For instance, with such devices, you would also need batteries (and phones) that are compatible and receptive to such quick charging. If not, our existing line of phone batteries would be prone to blasts and catch fire. (We already hear about such incidents!)
To that, there are also technical limitations in accommodating the cooling system on the charger that is essential to cool down the phone and absorb the extra current.
In addition, fast-charging batteries also get discharged rather quickly due to their limitation in the storage of energy.
We do have chargers and batteries of high capacities that charge quickly. But they are far from being used in Smartphones. Among many things, they are used in radio controlled model airplane.
(Courtesy: Digital Trends)
Battery technology has come a long way since the beginning… particularly in the Smartphone market.
Only last year Oppo released its R17 Pro, claiming that in just 35 minutes the dead battery can be charged full.
So, comparing to the old days, we have come a long way. But evidently, there's still a lot of room to improve and a long distance to cover.
Hope this answers why we don’t have devices that charge our phones instantly.