I could not find specific information directly explaining why Murcia Imperial is ineligible for promotion despite finishing first in Subgroup A. However, there are common reasons why a team might be ineligible for promotion, such as not meeting financial requirements, having issues with stadium facilities, or being a reserve team for another club in a higher division, which often leads to automatic restrictions on promotion to prevent conflicts of interest.
If these general reasons align with Murcia Imperial's situation, they might explain the restriction. For a more specific and accurate reason, it's advisable to check official announcements from the league or club, or local sports news sources.