Exported file size much larger than original source video?

I apologize in advance if I'm using the wrong nomenclature to describe this problem, I'm a neophyte and I'm learning as I go along. I think my problem is a pretty basic one though, hopefully this makes sense.

When I take a clip, let's say it's a 500mb MP4 clip - I'll go in and make my ends, usually I crop out 25 minutes of video down to about 12 minutes or so, so the majority of the video has been purged out using ripple deletes, etc. I don't add anything to the videos aside from canned transition effects here and there - there's usually 5 or so per video. The problem that I'm noticing is when I go to export these clips into MP4 format, the file sizes are coming in at about 300-400% higher in size than the original clip... despite half the clip being cut out. Can anyone maybe clue me in as to what I'm doing wrong here?

If it's helpful, this is no high res footage, usually 720p video.

Try to compare the original file resolution and bitrate with the resolution and bitrate that are set in the render options in DaVinci. If you already have a rendered file compare those values in the original file vs the newly rendered file. You are probably rendering the new file in a higher bitrate and/or a higher resolution than the file you started with

As an example, if your video has say a bitrate 10000kbps there is no point rendering with a much higher bitrate, you wont increase the picture quality You can therefore set that figure in the render settings so your file should not be huge. The picture illustrates what I'm saying.

Thanks guys, the bitrate does appear to be the issue. I'm seeing everything from 1600-2600 in most of these files and the default rate is obviously waaaaaay larger. I did some test runs with lower bitrates and I'm seeing the results I was hoping to see. Thanks for y'all's help.

I wish there was some mechanism where it would automatically adjust to the source video - that would be pretty helpful.

File size = bitrate x duration.

You've made the file shorter, so the only explanation for the larger file is a much higher bitrate than the original.