There couple reasons for it.
1) Wildfly (formerly JBoss AS) and Teiid is completely separate open source projects, they are managed completely at different timelines.
2) JBoss EAP is product Redhat sells subscription, has completely different licencing model. Same thing with time lines and teams and contributors.
So, there is no way to bring build together so that the JBoss EAP has Teiid versions. That is why we take plug-in mechanism. But if you are Redhat customer, Redhat productization team just does exactly same as what you are asking, check Redhat JBoss Virtulization http://www.jboss.org/products/datavirt/overview/ You can download this for free and use, however this is also under different licensing model, and restricts its use for production purposes, unless you have Redhat subscription.
The issue with resource-adapters is bug, it is been logged as [TEIIDWEBCN-9] Resource Adapters not visible in web console - JBoss Issue Tracker