Evaluating projects that don't meet the requirements?

If it looks like they really tried but don't understand it, it would benefit them if you explained where they went wrong and how they could improve their project. Even if they don't completely understand what you're telling them, they will have gained some insight and can ask more specific questions about what they don't understand. However, if it looks like they made no attempt at all, I wouldn't see a problem with just telling them to try again. There's no need for an explanation of what they did wrong if they didn't try.

Many students have problem with meeting the requirements. Sometimes it's just a small thing, like not having made enough shapes. In that case I tell them: "It looks as if know how to do this, but the requirements are such-and-such, and I'm sure it will take you no time at all to comply." Once I did pass a project that lacked one shape. The rest of the program was beautifully executed and showed a sophistication that went beyond the expected. The existing shapes were also balanced so that adding the necessary shape would in fact have ruined the visual impact. But I did explain to the student why I did not demand that extra shape. If there is a misunderstanding about how a piece of code works, I try to explain. Other times it's a lack of understanding of the subject. The resizing project tends to be classified as "needs more work" due to lack of understanding. If a student is close to passing (variables where there should be, and getting at least two shapes to move correctly compared to each other) I would take the trouble to explain and try to point to an example of a resizing code. Or make a program to show the student like you did. If the student has put in an effort to get it right, but has major trouble I would try to point out the biggest flaws and often explain how to make the project easier (as many students try to combine ellipses and rectangles in the same program without using Mode commands, for instance). If the student has not even managed to insert variables in all the shapes to be resized I would tell then that this is the first step, and encourage the person to watch the videos again.
Resizing was the first CS problem that had me struggling so I accept that there are others out there that probably have to work their way through this subject step by step. I was not ready to take in the whole picture until I'd broken it down to bits I could grasp. I've also had very little success presenting other users with a formula for resizing, even with copious comments in the code.
But I would not just say "Try again" and move on. It's always about helping them a little bit along the way, I hope.