Google is not going to tell anyone what determines how they drop a site over another one.
Probably not... would give the inner workings of the black box away, but I have noted that in general the sites most affected are those which are REDUNDANT, ie. superfluous, repeat, more the same, nothing new, been there done that, etc.
The web is a big place. A Very Big Place. And even giant G is not up to the task. Of Indexing All. Bing makes no bones about what they include or why some internal site pages don't appear: redundancy, but Bing does attempt to list all home/index pages.
We had the Farmer change at G some time back which was cheered when it appeared which tackled the MFA, scraper, thin sites. That happiness lasted about 6 months before Panda 1x through 2x hit.
<smiling>I step away from this discussion for a few minutes and we're now talking about adding blinking lights ala 1990 (animations, images, video) to make our sites stand out? Images? Scratching head... the top SEs are pretty good these days, but even they can't do pics or vids worth a krap... only the text content has any assurance of site content/intent/value and that will be the significant part of how a site will rate/rank.</smiling>
There are no real answers for why one is hit by Panda unless one is honest in their appraisal of their own site. That's like asking parents to rank their kids as regards suitability in human social terms. However, we can always diversify and expand, just like we can educate our kids the best way we can. That's where the time, energy and funds should be expended, particularly if this is business site.