Salesforce stock is down with the rest of the market and not as appealing as an acquisition tool as a result (they also paid a lot for slack). They also already play in Zendesk's space (eg service cloud) and tend to buy what they don't already have.
Ehh....in the time I was there, they bought Tableau _and_ Datorama in the same month, and they already had reporting/analytics features (although not as in-depth).
They also bought a dozen or so machine-learning companies that all did similar (or even identical) things over the span of the 5 years I worked there.
Famously, they bought Heroku, and then completely ignored it (including internally -- there were efforts at one point to have Heroku be the "way forward" for internal development on PaaS providers, and they scrapped that entirely while keeping Heroku more-or-less running).
I'd say Salesforce tends to buy whatever shiny thing gets Benioff's attention for the moment, usually because he talked to somebody at a conference. The guy tends to ram through quite a few questionable business decisions, and these days Bret Taylor's job as "co-CEO" is mostly "cleanup crew" for Benioff's various whims.
Do you have examples of this?
Stuff like Benioff's "just the tip" tweet has always been who he is when his handlers don't have a tight grip on him. Bret Taylor's position seems like he's been put there because 1.) He's got _some_ engineering experience more recently than 1999, and 2.) Bret is less, uh, belligerent than Benioff.