Adam Clarke on Joshua 22:26

An altar, not for burnt-offering, nor for sacrifice - Because this would have been in flat opposition to the law, Lev 17:8, Lev 17:9; Deu 12:4-6, Deu 12:10, Deu 12:11, Deu 12:13, Deu 12:14, which most positively forbade any sacrifice or offering to be made in any other place than that one which the Lord should choose. Therefore the altar built by the Reubenites, etc., was for no religious purpose, but merely to serve as a testimony that they were one people with those on the west of Jordan, having the same religious and civil constitution, and bound by the same interests to keep that constitution inviolate.