Because two of the three bureaus will simply tell you to contact the creditor who made the inquiry. The other may or may not respond favorably. Furthermore, inquiries are not actually "reported" data but are just records of requests by creditors. So if there are unauthorized or unwanted inquiries on your credit report, then the real problem is most likely with the creditor who placed the inquiry (not the credit bureau).
So the best approach to removing inquiries is simple: dispute directly with the creditor.
If the inquiry was unauthorized then you can simply state the facts, and demand that it be removed. You can also mention that the FCRA allows for $1000 in damages to be awarded to consumers for each unauthorized inquiry. That ought to get their attention.
There are other ways to address inquiries that we haven’t covered here, but this is by far the best and most direct approach for most situations.
The main thing to remember about inquiries is that if you dispute with the bureaus you’ve got several disadvantages working against you right from the start. Your chances are a lot better if you go to the company that placed the inquiry and demand its removal. Disputing directly with the bureaus in an attempt to remove inquiries will generally be wasted effort (except in a few rare cases).