There was a very important item in the article referenced by the OP. To wit:

"...in 1997 it was agreed that Russia would be allowed to base its fleet at Sevastopol for 20 years."

Knowing that this agreement with Ukraine will expire soon, it appears that Mr. Putin saw his opportunity to seize Crimea when a new, weak government took over Ukraine. Why not? In his view, at least, the benefits far outweigh the possible costs.

Bev and Jerry