Because languages with the same speed are generally a lot less flexible. If you have access to allegro CL or LispWorks and you and your team know CL you must ha

Because languages with the same speed are generally a lot less flexible. If you have access to allegro CL or LispWorks and you and your team know CL you must have some very good reasons not to use it. SBCL (the implementation they use) was(is?) known to have a pretty bad GC situation.