Whether or not AT&T was far-seeing, they had a mandate to design and deliver universal telephone service, and cost-plus deal to pay for it, so it made sense to buy nice expensive things. Even when the mission was fulfilled and the economy started to restructure the company, it ran along for at least another 10 or 15 years before the real disruption started (the 1996 breakup that turned Bell Labs into Lucent). And even then, the labs contributed fundamental research in machine learning, quantum computing and databases, to name a few areas. As you say, that model of large-scale corporate R&D doesn't exist any more - there's no funding model to support it.