On a professional, technical, Forum like this I suspect nearly everybody understands "why" it's done, but it still feels childish and just a bit disrespectful. Perhaps one reason it feels that way is because you're not aware of the circumscribed boundaries until you transgress and get your knuckles rapped. At least, when I registered a few weeks ago I wasn't aware of the restrictions until my unsuccessful attempt to post an image. It's embarrassing to compose a post containing phrases like, " . . . as shown in the attached screenshot image . . . ", and then . . . . discovering that you can't attach an image!
(And here I'm supposed to chastise Chris and the other moderators for not sending a succinct but detailed notice to new members, outlining the "Regulations of New Members' Purgatory". But if I'm honest with myself, I may not have paid much attention to such a notice even if it was delivered on a silver platter by a scarlet-coated postillion.)
I have observed very little consistency in this regard among the various professional Forums where I participate. In one case, all of your posts must pass through a moderator before appearing on a discussion thread - perhaps a day or more after submission. Another requires current members to vouch for you before you receive normal privileges. Others limit the length and frequency of your contributions. Or restrict you to only plain-text submissions (no links, images, formatting, or HTML tags).
Around here the rules seem to be reasonable, though not widely publicized. I can't tell if they are applied uniformly or not. Moderating a Forum like this can be a tough job, and I'm grateful for those who have put their time and efforts into doing it!