You get an achievement for matching 20 times. Being able to match more mounts only gets you there faster, which is nice IMO.
It would really suck if rewards from a possibly one-time 3mo event were made effectively unobtainable for people who haven’t played the game consistently for 20 years to obtain every possible mount, including shop, one-time events like pre-patches and remix, promo and cross-promo (ex.: D4) mounts on top.