The transition isn't free. Additional software means more technical overhead. Now you need to worry about training your teams to understand and maintain an Access DB instead of pure spreadsheets. You'll now also have to worry about hiring people who'll be able to adapt to the new system. You'll probably need to hire a full time DBA too.

Also, if it ain't broke, why fix it? I feel like a transition to a new system at times is akin to a software rewrite.