Because you don't know what your user wants to do and eventually you'll annoy someone

What if I copy something but accidentally get another couple words one of which is a number. For example copying from a chat app and get the date with the message. Then my "Sep 24th 416-555-1234" input which, would have been very easy to fix, becomes 244-165-5512 34. It will take me a few seconds to realize what has happened, identify where the intended phone number starts and remove the accidentally pasted digits.

The nice thing about the native input is that it is very simple, predictable and flexible. It may be easier to make a better UX on the happy cases but it is very difficult to not add some suboptimal and confusing UX on the less happy cases. Often times it is best just to keep it simple so that the user can easily complete their task rather than adding some "magic" which may backfire and confuse users.

It is surprisingly often that I need to open a text-editor or clipboard-editor to format values before pasting them into apps or websites because they have broken an input field by trying to be magic and failing to consider anything but the happy cases and maybe one or two bad paths.

I was talking about numerical amount fields, not phone numbers or dates or credit card numbers. Those are different things entirely.

FWIW if you're copying text on Android, you can tap the clipboard popup to edit the clipboard item before pasting it elsewhere.

The exact same problem applies. If I copy "Sep 24 $2412.45" out of a message and you quickly "clean" it to 242 412.45 I may not notice and even if I do it will take a second for me to realize what happened and clean up the value to be the intended amount. If I see the original text in the field it is much more obvious what happened and quicker for me to understand what I need to do to fix it.

> FWIW if you're copying text on Android, you can tap the clipboard popup to edit the clipboard item before pasting it elsewhere.

I never noticed that after 13 years of Android. I checked that now and I could not find a way to do it. Samsung's keyboard has a way to look at the clipboard but I could not edit them. Swiftkey does not. Maybe Google's keyboard? It's not on my phone. I looked at a couple of videos but they don't look anywhere like my phone. Not a feature to invest much time on it. If I have to edit the clipboard and I can't do it where I want to paste it, I open an editor and paste it there.

I'm using stock Android, Pixel 8 Pro. Highlight text then tap "Copy". See a toast in the bottom left. Tap on it (not the X) and a little text editor applet opens up. Here you can edit the text and save it, updating the value in the clipboard. Then using Gboard, it has clipboard history so you can see and paste the specific recent item from the past hour that you want. (Unfortunately it can't be edited after initially copying although you can long press them in the Gboard menu to pin for longer or delete them).