MicrosoftOK, I am not an employee of Microsoft, or an MVP.
But I wouldn't expect it to compress the images -
That would require loss of the detail in the image, and user indication of the form of that compression.
Remember that the presentation of data is according to the format detalied for that presentation of the data accessed by Excel from the storage, workbook or other storage.
and there are facilities within Excel to have an image (as thumbnailed in a cell) to be presented as any acceptably specified size and format, as well as the actual size -
pixels or twips, cm, or inches, within the physical limits of the device used for that presentation.
And also - the appropriate colour depth of the image and the display device, and the image ( video, or print driver) used to direct data to that device.
Or - simply - the image as stored and accessed by excel is not likely to be adjusted to fit the presentation requirement you indicated to Excel itself.
