Understanding this decision requires understanding Pivotal more broadly. EMC (which owns VMWare, which owned Spring) bought Pivotal Labs (primarily a Ruby consultancy) and used the brand for a new spinoff company (Pivotal Software, Inc). That spinoff company received as its founding endowment a hodge-podge of enterprise software technologies they had acquired over the years - Spring, RabbitMQ, CloudFoundry, Greenplum - and the consultancy, which is still called Pivotal Labs. For the most part they put the Ruby consultancy people in charge.
Even though Pivotal Software is an amalgam, Pivotal received most of its culture from Pivotal Labs. To the extent that you can anthropomorphize a corporation, it really, really likes Ruby. Because of CF, it's warming up to Go fast. Spring is too big and important to neglect. But it's hard to see how Groovy/Grails fit into the big picture. It's not in vogue with the top decisionmakers and it's not critical to the business - it's just something that tagged along with Spring. I doubt anyone has any idea what to do with it.
You'd also need to understand that not all full-time Groovy and Grails developers make equal contributions. Funding the 2 technical workers on Groovy might make sense for a business, but due to ownership problems related to the brand, codebase, support, channels, and what not, disentangling these 2 workers from the whole mess is a legal nightmare. Perhaps there's something similar with Grails, but I don't know much about that one. Pivotal obviously decided simply terminating funding was more profitable than trying to split off a separate business and sell it all to someone else.
Even though Pivotal Software is an amalgam, Pivotal received most of its culture from Pivotal Labs. To the extent that you can anthropomorphize a corporation, it really, really likes Ruby. Because of CF, it's warming up to Go fast. Spring is too big and important to neglect. But it's hard to see how Groovy/Grails fit into the big picture. It's not in vogue with the top decisionmakers and it's not critical to the business - it's just something that tagged along with Spring. I doubt anyone has any idea what to do with it.