There were many consolidations on the telecom markets during pre-NFV era. It was good for the major vendors, but might not be equally good for their customers - the telecoms / service providers.
End-to-end solution from one vendor is safe, but how should a telecom compete? It is difficult to introduce components from another vendors even if they provide some innovative features. When a solution lifecycle is 5-7 years, you cannot easily switch to an alternative. You would think heavily before changing expensive appliances more often. It is also difficult to integrate technologies from different vendors - the solutions are usually designed and integrated by the vendors themselves.
Internal capabilities of the telecoms shifted to operational excellence, while the ability to innovate decreased.
The logical decision of the major telecoms was to force vendors disintegrate their solutions. The key point is the introduction of standardised (NFV reference) architectures - models with requirements for the standard building blocks with standard interfaces between them.
When we say NFV ecosystem, we mean that components from different vendors work smoothly as parts of the integrated telecom architecture, and can be exchanged relatively easy without loss of quality and functionality. This makes the telecom landscape more open in comparison to the highly integrated end-to-end solutions from the preffered vendors.
Even in the recent examples when the leading telecoms delegate much of the NFV ecosystem to a single vendor, the picture is different. The experience, which the telecoms get in the first waves of NFV adoption, makes it much more easier to disintegrate later, but get the most of the early NFV adoption now.