As a former customer of Joomlart and someone who runs a larger-side Joomla site. Let me give my insights. J5 is great and the best version of Joomla ever. Yes Joomla's market-share is smaller than what it used to be. But there are still some die-hard users of the platform.
Personally I never plan to leave Joomla unless it ends. And I run a large independent TV & Movie streaming website using J5. And we began with J1.5.
Personally I hate page builders, I think they take away personalization for a dev or coder. I like using my own custom CSS and HTML to customize my site to my needs.
We use Helix Ultimate (because it's the standard-bearer when it comes to a template, nothing against JA but just my opinion after switching), MyShortlist and YooTheme Zoo & Widgetkit. And everything else is stock Joomla. And then we use the HTML blocks in each extension to customize to our needs. Custom CSS & Overrides are your friend also.
The issue is many Joomla template & extension providers are just giving up because they see a mass-exodus. It's not a mass-exodus. The issue is the free versions of templates are enough with Joomla out of the box. The market-share of Joomla vs Wordpress has stayed the same since 2020 and is still 2nd to Wordpress. Now yes J5 brought mass changes and some J extensions and template providers are using the changes as excuses to not update or make the changes. (See K2 for example and the biggest excuse ever their owner gave claiming that Joomla is dead due to its changes and requirements).
At the end of the day Joomla is still thriving and actually needs its developers and people who run Joomla sites to be innovative. The other issue is the extensions and templates have become very stale. We need to see new stuff and innovative stuff again. Page-Builders were the next big thing when they arrived and people who don't having expert coding-skills they are perfect for and those of us who have coding experience choose just to use templates. Now it's time though for the devs to create the next big thing to rejuvenate Joomla again. Competition creates good business and right now there is zero competition.
And I'm gonna give the best example, a few months ago I saw a new product called GK Framework run here on JA. I was really excited about the possibility of a more lightweight framework that was 100% customizable and more vanilla. Nothing but bugs and it now seems to have been abandoned. Last update was in April of this year, yet the same bugs still exist that I posted about months ago in that forum. GK Framework was a genius idea that just everyone seemed to have forgotten about. And I would've made the switch, I even purchased a subscription for the Sway template based on it as I loved the sidebar menu and had to cancel a day later due to it not working YooTheme extensions and tons of bugs. And that is a major issue with a lot of providers is nothing seems to be tested with other providers extensions. Some people like to mix-and match providers (different template/framework and extensions). And for one I'm really sad because GK Framework had such hope in its concept.
If Joomlart wants to continue, I would focus on be different, again competition creates a healthy ecosystem. Maybe someone wants to use a hypothetical T5 Framework but extensions from other providers. Make sure it works. Astroid Framework is the biggest challenge to this as I've tried it in the past and it WILL NOT work with Zoo or Widgetkit at all and they refuse fix anything trying to blame YooTheme when it is literally a backwards issue with J3 in their code that is causing the issue.
I'm hoping Joomla picks back up with providers and extensions. I love this platform and it's perfect for what I wanted to create. Yes Joomla is becoming better overall. My Pagespeed tests went from a C grade with J4 running JCH to a A grade with J5 without JCH installed. That should be the focus for all providers is J5. The old expression out with the old and in with the new. J5 has been out for a year now and develop for the now. But again be innovative, time for good competition. Make me want to or give me a reason to want to try your templates or framework vs someone else's. Right now it is very stale, I use Helix and don't have a reason to leave. I did with GK Framework but it was a mess and has so far not been corrected.
Maybe it's even time for GK Framework and T4/5 to merge and become a lightweight framework/template, something to make people want to use JA over someone else. Just an idea because I prefer a more lightweight, customizable template/framework over a bloated one that has more features than what I will ever use. I want a template that I can edit files and not have to worry about hem being overwritten by a new update every month or few months. MJGA (Make Joomla Great Again).