Simple. Chassidim don’t feel Agudah represents them and they didn’t feel the Siyum was meant for them. I know many Chasidish people that finished Shas and did not attend Metlife. Kal Vechoimer for those that did not finish Shas. How many Lakewood people would attend a siyum made by the OU? Therefore when offered with a nice alternative they grabbed it. Even Belz, which is officially fully part of the Agudah, did not feel the Siyum was meant for them.
And proof of this, is by looking at the difference between Metlife’s program and Dirshu’s. Without going into any specifics, it’s obvious that Metlife wasn’t catered for the Chasidish crowd, while Dirshu was. Meir G says that isn’t true since the speakers were majority Litvish by Dirshu. However Chasidim have absolutely no problem with Litvish speakers, while the Metlife was a step further. And I don’t mean problem in the literal sense, only regarding whether it catered to them or not. That’s all besides the point that there was no mainstream Chasidish speech at Metlife. R’ Aharon Shiff was bought in as the Rav of Antwerp and Noviminsker Rebbbe isn’t mainstream. Again, not that Chas Veshalom anyone has a problem with any of the speakers, they just felt “Men maint nisht mich.”
It became similar to Israel where there is a separate siyum for the Chassidim and a separate one for the Litvak’s.
I don’t think it has anything to do with the fact that more Chasidim do Dirshu, if it’s even true…
Edited