It could be because personal loans are coded as consumer finance accounts (CFAs) by the Fico algoritim, and the Fico algoritim views CFAs as a negative item. Consumer finance accounts are generally (not always!) indicative of a high-risk borrower. 
It could also be that the loan lowered your AAoA.
I could very well be wrong about this, but that's what I think.
@Anonymous wrote:
An unsecured loan is a loan with no form of collateral (personal and student loans fall in this category). A secured loan is backed by some from of collateral (mortgage and auto loans are the most common). Consumer finance accounts are generally sub prime and indirect lending loans (examples include financing from furniture and rent-to-own type businesses).
The inquiry, drop in average age of accounts and having 100% utilization on a new loan will all factor into scoring. Any one, or combination of these things can lower your scores.
To add to this excellent list, depending on your scorecard it might've reset Age of Youngest Account too and that's yet another penalty potentially.
