its more that watering directly probably produces bigger drops and they can damage the foliage. A very heavy rain shower does batter plants. I have often thought the same thing about advice not watering directly in sun. you will get some sun scorch but that is what nature does.

by watering at the base the roots will get the water quicker more directly.

Because plants in the garden are often planted where nature never intended. The rain on the leaves is fine; It's when the sun shines...the droplets on the leaves acts like a magnifying glass...burning holes or damaging the surface so they're not able to absorb/process nutrients. So, if you do water; water beneath the leaves or when the plant comes into shadow.

I hate to say this, but its a myth that water droplets on leaves act like a magnifying glass causing burn damage. If you think about it, were that true, all plants in the UK would have burn damage because we get frequent showers followed by sunshine. This article (there's a load of others debunking this myth) mentions it

https://www.theguardian.com/lifeandstyle/2017/jul/23/dont-water-plants-on-sunny-days-and-two-other-horticultural-myths

I tested it myself once after I heard it was a myth - I picked a hot sunny day (30degc) and deliberately left water droplets on some plant leaves in the sun. Nothing happened, they were fine, even the textured leaves, which retain the water for longer.

One of the reasons not to pour water onto the foliage is if it contains any liquid fertilizer - that can cause damage to the leaves as the fluid evaporates, but mostly its because the roots need the water, not the foliage, so its a waste to pour it over the leaves when its possible that not enough of the water actually reaches the roots. But otherwise, it is as Seaburngirl says - there's a difference in the force of the water if its from a watering can or a hose running at high pressure compared with normal rainfall or a sprinkler.

Never happens here in the desert, and many of the larger wholesale nurseries water with sprinklers, including in the middle of the day.