Reply to iTunes doesn't show BPM

Well .... I'm starting to lose hope for the existence of any consistency in terms of tagging files ....

I'm just starting to arrange my songs on iTunes ....
I saw that iTunes does not show the BPM of the files, unless i analyze them first in Traktor...
1. I Analyzed all of my songs ...
2. I loaded some of them into iTunes to see if everything is OK...
3. Some of them have the BPM shown and some don't ... (In Traktor the BPM appears in all of them)
4. I did not find any difference between the files that iTunes shows their BPM and those that iTunes doesn't...They're all the same format & from the same folder ....
5 (and a bit less to do with). If you have any general tips for making life easier when arranging songs on iTunes and Mac .... I'd appreciate it...

Thank you.