Stating that SCMMs are the main reason the game failed is biased, and so is saying that they ruined the game. But this is not a thread to debate SCMMs, nor is such heated debate allowed, and thus, I end that line of thought here.
The truth is that there isn't as much staff on MQ as there was when the SCMMs first debuted. Back then, there was Warlic, Mae, blues, J6, and Korin (and several more) at the height of MQ, all able to handle releases large and small.
Given that staff had been taken and not replaced, everything has declined in terms of quantity, and in some areas, such as SCMMs, quality (as far as specials and lack of specialization; visually, they're still relatively exclusive). SCMMs should continue, but with more spacing between releases, so as to give the current Staff time to better plan them out and work on them little by little.
On that note, SCMMs wouldn't be the only things SCs look forward to if there was more SC-Only content that had some relevance outside of War/Holiday Event missions, such as what the Dragon Egg Saga is to DAH/DL members, or bringing back Planet Previews. However, it's more time-consuming that just one mech, so it will not be likely that we'll see such events in the future, with the exception of maybe SC-Only Planet Previews (since the planet could be released to SCs while still not complete for a full release).