There are many ways to make smaller screencasts.
Record a smaller window – don’t record your software fullscreen on a 4K monitor – around 720p should be eenough for most applications. Or crop unneeded areas if you just need part of your screen.
Reduce the frames per second – depending on the recorded software 15-25 fps should be plenty.
Encode with variable bitrate. You don’t need constant 2500 kbit/s or more bitrate when there’s just a bit of mouse pointer movement.
I like Handbrake for encoding – something like this should work:
H.264 Profile high 4.1
Preset: medium or slow
Tune: Animation or none
Constant quality RF 22 (or higher RF for smaller files with less quality)
Audio AAC 64kbit mono if theres just voiceover or 128kbit/s stereo
Framerate 15 FPS peak