One possible big reason for BIAB to keep its classic aka legacy looks could be the very super low PC requirement.
While BIAB web page mentioned a fairly up-to-date PC hardware required, the minimum OS preferred is Windows 98 on at least 256MB available RAM. This could limit the choice of programming tools to write BIAB.

IMHO there are hardly anyone still using 10 year old OS to run current new BIAB. Old CPU and bus speed would stutter just to play back melody.

I would suggest that for new release of BIAB, the minimum required is a 5 year old PC, i.e. XP and 512MB ( and the equivalent in Apple OS).