For twin tail day specifically its 2/2 because twin tails have 2 bunches of hair. IDK Japan likes doing a lot of weird holidays like this.
It's not really a holiday, more of a small pop culture celebration in certain circles due to their love of date puns. It's similar to how online shopping apps might hold regular sales on matching day-month dates wherein it doesn't have any significant history or recognition outside the cultural circle.
Most recently, Feb 22 is "Cat Day" or 猫の日 for the wacky reason that there are three 2s in the date that are pronounced as "ni" normally, but can be "interpreted" as "nya", which is the Japanese onomatopoeia for meowing.
These dates are most celebrated by content creators because of their target audience and it gives them a theme to work with. However, there are also cases where some of these dates are boosted in significance by commercial entities to the entire country and possibly beyond, for example Nov 11 which is Pocky Day in Japan and Singles Day in China.