including the size of the games in html5 compared with swf. I guess the change in the format is related to add more content to the games and animations (thing u can't never do in a swf games).
I think you are interpreting "size" the wrong way as if it directly translates to more content.
Even if you look at a lot of MNF older games (in swf) there is a lot of them which have more content in itself (scenes, gameplay, story, etc.) and at the same time they're 10x smaller in size compared as if they were made in html format.
Newer or different format not always means it's actually more efficient in what it is supposed to do. Especially when your goal is to make simple small 2D game. And as the joeyeroq mentioned above, requirement to rasterize vector graphics to raster images which have to be defined pixel by pixel in html masively increased the size of all new games. And while vector images can lack detail compared to real life photo images (as this format is focused on geometric shapes on a coordinate system) that's completely not the case when we plan to work on simple 2D images used in MNF games.
For example you can no longer easily zoom the graphics or easily manipulates certain elements in html as it was possible with SWF. Now it has to be specified by additional lines of code, which depending on the person could add more time to the making process and it's easier to makes mistakes.
Basically we lost the small size of the games (format) and certain simple key functions which were perfect for the job. And what you get instead is bigger size of the file and more potential tools... which really are not necessary to get the job done :/
If I had to translate it to something simple, it's like you need to decorate a simple cake (MNF game) and u could use either SWF (small spoon) or html (shovel). You can do it with both things, but one will work better than the other.