At that time, the Japanese navy hoped that two fleets would attack Wright Bay from north to south, so they needed two fleets to take the San Bernardino Strait in the north and the Surigao Strait in the south (it seems that these two roads are the only way). The San Bernardino Strait is close to the American fleet, so it is very likely to be attacked by air. Kurita's main fleet is certainly more resistant to fighting. The main fleet attracts American aircraft, and the detachment can be protected from air strikes.

If the team goes north, once the team is wiped out, even if the main fleet reaches Wright Bay, American ships can escape as long as they run in one direction. Even if the main fleet suffers some losses, the damaged main fleet+detachment can still form a siege, thus ensuring the annihilation of American ships in Wright Bay. In fact, except for the sinking of Musashi, the main fleet did not lose any important ships.

The above is purely personal speculation.