They tried.
Many states had extensive land claims in the west - Connecticut claimed a band of territory bypassing New York and stretching to the Pacific, and sent settlers to what is now Pennsylvania's Wyoming valley and the area around Cleveland in Ohio. Massachusetts made a similar claim to portions of Michigan and western New York, while Virginia claimed the whole Old Northwest (or modern Midwest).
In this context of overlapping territorial claims based on unclear colonial charters, which at times even led to bloodshed, and the prospect that those states which had extensive western claims - already the most populous in the union - would gain even more lopsided influence, congress acted to create new states out of most of the disputed territory. (The rest became the western portions of New York and Pennsylvania.)
Actually they did, however the Northwest Ordinance reorganized them as territories. Wikipedia ( I know not the best source but has a nice illustration) has a nice map showing how the states claimed the west. The old Southwest would also be ceded to the federal government after a dispute with Spain was settled. This was to allow for the creation of new states and better organized systems of governance in the region.
This map shows them extending infinitely to the west.
