Let me clear up what appears to be a fairly common misconception, when it comes to "next man up" for games and such, that next girl or boy up is typically going to come from the younger 1st team and not the same age 2nd team at the ECNL/GA/MLS Next level. If you think about the Clubs' focus on winning that makes sense, why would you bring up an end of bench player when you could bring up a player near the top of your lineup.
Now I get that a Showcase is different but still the Club's priority is going to be to their ECNL players (no offense but it is an ECNL showcase and not an ECRL showcase). Would it have been a nice gesture to bring up an ECRL player? Absolutely, 100%, but there was no obligation to do so unless players were told otherwise. Does ECRL not have showcases they can participate in? I thought they did. If your looking for equity you're going to be sorely disappointed in youth soccer.
Additionally, its not uncommon for showcases to include U15/2007 teams (MLS Next does) as many of these kids are in HS (I have an 07 still in 8th) and they will draw interest from coaches.
Dose of reality here, ECRL/DPL/EA are typically not stepping stones to ECNL/GA/MLS Next teams. The former is more marketing of a carrot on stick than anything else to separate you from your $$$.
Now should it be different, yeah probably, but that's the reality. We can blame clubs all we want and they deserve most of it. But again, by the time your kid reaches this age group you should know better. We all have to be more realistic about our kids abilities (particularly in relation to other players in the program) and consider that in light of what we are promised by the club.