Pardon if some of this seems to be lecturing ... not meant to be ... but I do know many tend to forget/ignore the past ... and it has everything to do with this very topic.
What's the purpose of the software?
Moodle a learning management system .. which grew out of computer managed instruction, I remember those ... 'drill and kill' they came to be known to some.
Other acronyms to google: ILS, CBI, CAI, CAL.
WordPress is blogging software ... content management (am not downplaying WP, great stuff ... better than DiDa, Front Page, or plain old NotePad/BBEdit FTP 'publishing' to Web server. I used to hold the title of a 'web master' at one time. But still, not the same purpose as Moodle.
Why is it difficult to update or upgrade a Moodle?
It isn't. If you use git. Many of the flies and code that comes with
Moodle package (zip or tar.gz or git acquired) is for programmers/developers.
Now if you had a Mac or Linux, you could do this on your moodle code directory
to see what I mean.
find ./ -name moodle_readme.txt will find 6 such files in latest stable.
find ./ -name readme.txt will find 11 such files
find ./ -name license* will find 7 such files
find ./ -name \*.md
Same on wordpress files:
readme.txt ... 4 such files ... obviously no moodle_readme.txt files
license* 6 such files
The existence of such files is not poof of ease of update or upgrade, but
the contents of them might give you a clue/hint. Take a gander at them sometime.
Is it fair to compare Moodle LMS software to a WordPress blog software?
Not really ... answer the following for yourself ...
What can Moodle do right out of the shrink wrap for online instruction?
with no addons/plugin, etc. to core code?
What can WordPress do right out of the shrink wrap for online instruction?
with no addons/plugin, etc. to core code?
Should Moodle be as easy to update and upgrade as WordPRess?
IMHO, yes ... and it could be made to be ... using the same tool programmers/developers use ... git.
It's becoming ... more an more ... the exception of all software for those use.
A better question might be to ask, what's the threshold for that to happen?
By all means explore using Joomla/WP/Drupal etc. as a learning management system ... better yet, see about integration where one could use the 'best' of those with the 'best' of Moodle ... or any such software ... like Google Classroom ... now open to all users, not just schools.
My 2 'sense' ... nope, spelled it correctly!
'spirit of sharing', Ken