LinkedIn acquires Lynda.com

Yesterday, on Crunchbase, I could sweat that the Lynda entry said it raised it's series B at a pre-money valuation of $1B in Jan 2015, giving it a post-money valuation of about $1.2B. The LinkedIn acquisition at $1.5B then represents a poor cash-on-cash return, it seems.

I wonder why the company sold for $1.5B just 4 months after raising money at a $1B-$1.2B valuation? What does this say about the online education space?

If anyone has insights, I'd love to hear them in the comments.