The move is big on a relative, not absolute basis. The smart money knows that this economy cannot handle normalized (i.e., 4-5% on the 10-year Treasury, which are still kind of low by historical standards) interest rates. The yield on the 10-year has run up nearly 100 basis points since last August. That's a relatively large move in a short period of time, and it eventually bleeds into borrowing costs for everything and will force the Fed perhaps to raise rates faster than anticipated. That creates uncertainly, and if there is any consistent trait of markets it is that they shoot first, ask questions later in the face of uncertainty.
The VIX funds are a technical factor that might be contributing to short-term volatility but when this market is brought down (yes that's a when, not if) it won't be because of these stupid VIX ETFs.
The single biggest reason the market has declined recently, IMO, is simply because buyers are exhausted. Valuations are a little rich (and have been for a while), and a large amount of good news like the tax cuts, recent job gains, and corporate earnings have been priced in via the ramp. Then, when you get a break like we saw last week, that affects confidence and the whole dynamic in the market can change. The price action on Tuesday was classic bottoming activity (gap down after a bloodbath the way before, then rally for the balance of the day) but we those lows yesterday and the process has to start again.