Until you can come up with a counter to Garp going there because he heard that Roger mobilized, and a counter to Sengoku and Garp himself saying he refused promotions to avoid having to directly serve the CDs frequently,
It doesn’t matter why Garp went there, nor does it matter why he refused a promotion
At the end of the day Garp saved the Celestial Dragons because he and Roger are boot licking dogs, no Admiral was going to save these scum lol.