Leviticus 17:6
And the priest shall sprinkle the blood upon the altar of the LORD at the door of the tabernacle of the congregation, and burn the fat for a sweet savour unto the LORD. And the priest shall sprinkle the blood upon the altar of the LORD at the door of the tabernacle of the congregation, and burn the fat for a sweet savour unto the LORD.
God positively commanded in Leviticus 17:3-9 that Israel was to offer no sacrifice except at the door of the tabernacle at Shiloh. That altar was the only lawful place for sacrifice and worship for all the tribes on both sides of the Jordan. In it all had equal privileges, east and west alike.
To erect another altar for sacrifice and worship would be rebellion against the Lord and departing from God. Such disobedience would bring the wrath of God upon the whole nation and not only upon the builders. Those who felt they could not abide east of the Jordan without an altar for sacrifice should leave that land and share the possessions and privileges on the west rather than disobey.