The arrival of Visicalc transformed the toy personal computers into legitimate business tools and set Apple on its course for what would be the largest IPO in US history up to that point. No one saw it coming until it happened.
Once it happened, the Xerox brass in New York question how they missed it, and start to demand a return on the money they've been pouring into PARC. This is what led them to seek a partnership with Apple and the infamous Alto demos for Steve Jobs.
Meanwhile, the PARC folks start to realize that the rest of this now exponentially expanding industry is going to catch up to what they're doing faster than they can scale down their stuff into a commercially viable product.
Xerox takes a huge swing with the Xerox Star. It's a market failure for a number of reasons. IBM takes a little swing with the PC, and it's a huge success, but they don't control the software. The PARC folks leave to join the rest of the industry, taking what they learned with them.