Crop to size / Resize during export: different results

So in summary-

1) A Crop in LrC is to change the Ratio of the visible image 'shape' or aspect ratio- For 3000:2216 you would need a Custom Crop-

2) In the Export dialog is where you define the Pixel Dimensions of the exported derivative image file.

3) The megabyte size of the new file is determined by several factors-

-The Pixel Dimensions of the exported image defined in [Image Sizing]

-The 'Quality' of the Compression (that gets applied to a JPG file) in Export [File Settings].

-The amount of detail in the image subject.  (eg. a photo of tree leaves compared to a blank sky)

• In non destructive LrC, cropping in the develop module is a ratio not a dimension. In the develop module, this cropping is an overlay, the actual image is not touched.
• When you export, LrC is not non destructive,  and if you you specify the crop, (or actually resize) you are specifying size as a dimension,  then you do change the end file. And file size will be affected.
• If you crop in the develop module and do not specify a dimension in export, then you are likely to have a larger file size than if you do specify a file size (dimension) in export.

Note, that it is advisable to crop in LrC to the ratio that matches the desired export crop size, as to avoid interpretation issues.

Oh and some reference material (not complete)

• https://helpx.adobe.com/lightroom-classic/help/export-files-disk-or-cd.html
• https://rickmcevoyphotography.com/this-is-why-your-lightroom-reduces-file-size/
• https://shotkit.com/lightroom-export-settings/
• https://expertphotography.com/lightroom-export-settings/

And what I found about MaxPreps

• https://support.maxpreps.com/hc/en-us/articles/208774058-Photo-Video-Submissions

from that:

• Photo cannot be more than 5MB in size.
• Photo must be at least 300 pixels wide.
• Photo must be in .jpg, .gif, or .png format.

Do you have a link for requirement 3000x2216 pixels? I have never used this service.

I do see that they sell photos in small medium or large, and large is 3000x2216, so that it would make sense to upload to MaxPreps at 3000x2216 (and site will produce down samples). 

• https://support.maxpreps.com/hc/en-us/articles/202469870-Purchasing-Professional-Photos-

1. Small 600 x 443 
2. Medium 1024 x 756 
3. Large 2216 x 3000 

I also see in other peoples inquiry's about how to crop/resize in Lr, in LrC, in PS (largely not in the Adobe community, yours appears tobe the first) Always refer to 3000x2216