As you point out, the supposed VIX tracking funds, e.g. VXX, use futures.
But in addition to the roll issue with futures that you mentioned, there are problems specific to VIX futures funds.

Futures on soybeans, coffee, the S&P, pork bellies, etc for which it's at least in principle possible to directly buy the underlying, have a simple "no arbitrage" argument that determines "fair value" for these futures contract. To the extent that arbitrageurs work efficiently, this means that there is a known fair value for these kinds of futures contracts, which constrains nuttiness in these futures prices.

But you can't directly buy the VIX underlying. So, the no-arbitrage fair value argument doesn't work for VIX futures.
A plot of VXX along side VIX shows that despite the tickers differing by just one letter, VXX ain't the VIX.

Berkshire Hathaway FAQ

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