File size is determined by only two things - bitrate and duration. How many bits per second x how many seconds = total bits for the file. Your AE exports clearly had significantly lower bitrates than the PP exports. They were also not BD compliant, which means Encore had to transcode them, which means new files at new bitrates, and thus larger sizes.
You may really be exceeding the limits here. It would not be unwise to consider putting each tutorial on it's own separate disk, instead of all of them on one.
The thing is, the AE exports look just fine. (The tutorials are just a bunch of screen capture/software stuff.) I didn't mess with any of the default preset settings for H264 out of AE, but yeah, they must've been encoded at pretty low bitrates.
I wasn't aware that BD specifications have minimum bitrate requirements, so that would explain why I'm unable to decrease the bitrates within PPro or Encore. Thanks for the info on that. I just figured as long as the footage was at least 720P with square pixel ratio encoded in H264 or MPEG2 I'd be fine, but apparently not!
The tutorials are for my own personal use, so I'm not too concerned about decreased resolution if I am able to make the SD content fit. Otherwise, yeah, burning multiple discs is my only option.
Thanks for the prompt feedback.