Historians have argued ever since the Gallipoli campaign as to why it was not successful. I don't think that there is a definite answer to why it turned out as it did although there were certainly some major failures throughout the campaign for the allies and nothing seemed to go as planned although it seemed a very easy objective at first.

The allies were expecting turkey to be an easy opponent and that the campaign would be over very quickly, however the points at where the allies attacked are some of the most easily defendable places there are, with the Turks on the high ground and the allies on the low ground in a very vulnerable position. Troops landing on the Gallipoli peninsula became stuck on its narrow beaches and rocky cliffs.

The same with the naval attack on the small strait of Dardanelles, any ships that tried...