Because there is a lot of money flowing everywhere.
Total VC investment through Q2 2014 is on the order of $22.7B [1], so if this continues, the VC industry is likely to invest about $45B through the year of 2014.
At the same time, the total market cap of the S&P 500 is $17.5 trillion [2], and it's increased by about $2T so far this year [3]. Total daily volume in the S&P 500 is $1.4B [3]; in 3 weeks, more money changes hands in the S&P 500 than it does in 2 quarters for the VC industry.