well it is a design choice
Nethgui uses my scl module with up to scl php74
Cockpit uses the default rh-php collection, but at this day the version is rh-php73, in a future it could change I hope.
With cockpit I cannot do like I did before with NethGui, it is not possible to easily push your code inside an official package.
That it was the power of Nethgui, maybe it is because @davidep let the possibility to a developer to hack the code that I came a developer, who knows 
Cockpit is used by the enterprise and the community so we have to make a choice and for example the cockpit apache dashboard is not aware that you have installed scl phpX from my module (or my mariadb modules). We could do it of course because it is matter what to glob in bash script.
In the same way since you have manually installed my SCL PHP module we could let you able to use it also in the apache cockpit, at least for PHP74 because at this time we have no solution for official scl solution.
However except for PHP74, I do not see a lot of interest. Actually if you try to set the php version with cockpit or nethgui, the priority is set to cockpit, so the nethgui setting is not used for the php version.
I do not plan to update nethserver-php-scl module, I think the major (good ?) code has been imported inside cockpit and it is well :-?
My only guess is why the community is not asking for php74 inside cockpit.