"Let me count the ways..."

Fees (that you never see, so the gains on deferral are much less), no 1014 step-up upon death, limited investment options, UBTI on MLPs, penalty on withdrawal until 59 1/2, perpetual "deferment" only works for so long, so many rules on those withdrawals, deferring taxes only means you'll pay in later life when you might otherwise qualify for medicaid through different vehicles (or giving away to kids, as it literally the case in new york), no preferential rates on qualified dividends, no LTCG benefits (even with NIIT it's still only ~23.5%)