I think the pace of progress and innovation has, for better or worse, meant that companies can no longer count on successfully evolving only from the inside through re-training and promotions over the average employee's entire career arc (let's say 30 years).
The reality is that too many people who seek out jobs in huge companies like IBM are not looking to constantly re-invent themselves and learn new things and keep pushing themselves into new areas every 5-10 years (or less), which is table stakes now for tech companies that want to stay relevant.