Why would rational people expose themselves to economies that do this to them?

Amongst other reasons:

- the cost (in terms of wealth taken) of redistribution is less than the cost of letting things sort out (eg in fallen asset prices or lost opportunities)

- (for those with only a little accumulated wealth) the prospect of attempting to accumulate wealth -- but failing at it -- is very likely and the consequences of failing at it are very high

...though as always a specific situation requires specific analysis, and there's no particular reason to believe the math works out one way or the other in a given scenario (and, also, to pretend to know the shape of someone else's preferences).

You might be able to do better than means-tested (flat-rate payouts to everyone! minksy-style "employer of last resort" arrangements!) but the underlying dynamic doesn't materially change: (loosely speaking) devaluing currency by X% takes away a lot more wealth from billionaires then from dollar-menuaires; if programs A and B both result in X% devaluation but A is means-tested and B isn't the difference in "cost of program" to the wealthy would be a rounding error.