It seems to be debatable whether they really gained a lot economically. Sweden is export-focussed, and has suffered from the recession everywhere else. Though, to be honest, though I was thinking of things I've read saying Sweden was suffering economically anyway, seems if you Google Sweden+coronavirus+economy you find a lot of wildly contradictory interpretations of the same economic statistics.
This BBC article says Sweden has been hit 'less hard' economically than other countries, but the data it includes seems to show it's nevertheless been hit pretty hard.
After avoiding a Covid-19 lockdown, the country sees its economy shrink less than in other EU nations.
www.bbc.co.uk
Seems clear the 'herd immunity through infection' idea (which I've seen being relentlessly pushed by libertarians across the web since the pandemic began - usually with the standard 'I'm so much smarter than everyone else' attitude that libertarians tend to have) really didn't pan out. And Sweden did have the advantage of low population density, lots of single person households, a good quality centrally-run health-care system, and a
co-operative populous.
Whether having opted for a stringent lockdown or a more lenient policy like Sweden's, for the time being countries must rely on development of treatments for the critically ill, and continued physical distancing, hygiene, face coverings, and contact tracing, until there is an effective vaccine.
www.forbes.com