Here's a question for you, how many actual requests are in that forum with a reply "Yes, let me code that for you"?
The truth to the matter is that most extension developers are just regular forum owners who have taken the time to write and develop an extension for their own board, that they themselves needed. And them generally being the nice people that they are, are willing to share it with the community. Then there are ofcourse the devoted extension developers, that are developing extensions that are useful to almost every board. For example something along the lines of logo, gdpr, contact, etc.. And as far as I can tell, these developers don't get their ideas from the Request forum.
Also, if you're unfamiliar with the actual coding of an extension it's easily misunderstood how much time and work there goes into developing an extension, not to mention maintaining it. So requests that look simple on the surface, could require a lot of code and time. More time than the 'common' user would think.
So, seeing the changes are slim that request are actually being granted and someone turns it into an extension, people offer assistance (tone is indeed debatable) on how to achieve a similar behaviour without the need of yet another extension.
Let's not forget, that often requests are made by users not that familiar with and/or active on this actual support forum so even though they "did a search with no results", it usually already exists, or something close it.
- but a simple mention "Unfortunately your request is technically impossible to implement" should suffice.
And unfortunately, that is close to never the truth. Anything is possible, especially cause phpBB is open source and you can change the core yourself. So in the end, everything can be created, you just have to put (a lot of) time into it. So, personally, I would advise those users (and pretty much any other using wanting an extension) to look into learning how to write some of your own. There are quite a few good and solid tutorials out there, good development resources. For example, among others, the Skeleton Extension. And I've been thinking about this lately, to write some tutorials on my own but haven't figured out where to start. A tutorial so a novice user can get a simple extension to work and actually understands what he's doing.
Also, sending a private message for help is a noble cause, but one you will probably not uphold for long. Once you've written an extension or two, people tend to already starting pm'ing you for support or private requests. And that becomes very tedious, very quickly.
Don't misunderstand me, I completely agree with you on the tone that more often than not is present, but we also have to face the hard reality.