Saving psd files from different programs or different versions of same programs will impact the file size,
in Photoshop for example, it does save a lot of data into the psd, sometimes this data is related to
effects, vectors, masks, etc, but also related to file info RAW / EXIF / IPTC
You can remove the image info (RAW / EXIF / IPTC) by clicking File > File info > Advanced tab
Select the items on the list and click the trash can icon at the top right, click ok and save.
Another tip to make any psd smaller in case you need to send it over to someone, for example,
is just hid all layers and save the psd with the them hidden, this will make the file really smaller.
I hope this tricks help you