That was originally the plan, but the problem with the Anglo-Saxon fyrd (navy or land) was that it consisted of freemen who were also the farmers of the land, they had crops at home and couldn't be expected to be out on the field for a long time.

Of course we all know that William de Normandie was ready to cross the channel around August 12th but due to unfavourable sailing weather his ships were kept in port until late September. This of course was a delay long enough that the Fyrd had to be disbanded because Harold couldn't supply them any longer and they needed to collect their harvest.

This left the English channel open for an unopposed landing and the rest is history.

References:

Medieval England, 1042-1228 By Toby Purser

The Norman Conquest, by Richard Huscroft