Is there a reason why PM will not embed ICC Profiles into TIFF Images?
Well, the answer is because we haven't added it yet! In general it isn't a good idea to modify TIFF files by adding tags, but since we started doing this (in a safe way) for the purposes of embedding IPTC/XMP, we could extend this to ICC profiles (already thought about it). I'll see about getting this added for 4.5 but no promises (what sounds easy often ends-up being more difficult than expected).
For JPEG files, it was relatively easy to do since these files can be "spliced" for the insertion of an ICC profile (actually, it is a bit more complicated when you consider ICC profiles that are larger than 64K).
--dennis