"They do all like their little independent silos."
Because how many of those outsourcers staff actually work for them?
Not damm many.
The actual domain experts will probably be in sub-contractors, or sub-sub-contractors.
And under strict instructions not to let on that in fact your ERP/CRM/Mainframe/Payment system is in fact not being installed by Atoss/Crapita/SCS but Joe Blogss Contracting (who actually know WTF they are doing).