The Marley need the "coordinate" back for two 2 reasons.
*****Do not read if you don't want spoilers from Manga.*****
1) The Beast Titan's ability is far weaker than the true coordinate. He has that ability due to the bloodline that he inherited from his mother, the same Titan that killed Eren's mother, his father's ex wife. We see the Beast Titan struggle to control certain titans, for instance, when the one survey corpse member he detained in order to find out what 3D maneuver gear was. He had to exert extra control in order to get them to comply.
Meanwhile, Eren simply had to touch Zeke's mother's titan form and without knowing what he was doing all the titan's in the vicinity immediately began obeying his wishes to destroy her. Plus they left all the humans alone in the area for an extended period of time, while attacking the armored titan. They remained completely enthralled long enough for the Humans to get away. The Beast Titan is not capable of this at all.
2) The reason Marley never just all out attacked the Eldians behind the walls was due to the threat represented by the coordinate. If they hadn't left them alone the Fritz/Reiss family threatened to release the Titans inside the walls and annihilate all of Marley. Also, since Marley relied on Titans for their military might, they failed to develop other military technologies to the extent other nations (Mid-East Allied Forces) did. The Mid-East Allied Forces developed anti-titan weapons. Marley needs the coordinate to neutralize their enemies behind the wall and maintain their military supremacy over the Mid-East Allied Forces.