The article mentions that Rhode Island did that wholesale: "The Democratic-dominated Rhode Island government recently eliminated more than 30% of its rule volume by setting an expiration date for its entire regulatory code, forcing state agencies to start fresh."
Ah, good point. If you believe a particular regulation is useful and necessary now, why wouldn't you also believe it would be so in the future? You may not be in power to conditionally renew it. And from a pragmatic political perspective, sunsetting smells like compromise; the political base and interest groups generally frown on compromise. All of which may explain why sunsetting isn't as common as one would think, even if most legislators share the sentiments expressed in this thread (and I would presume that they do).
It's historically been hard to do because there's a tendency to just automatically extend the sunsets when they arrive. Though a couple of other replies to your comment have a couple of nice examples.
That suggests a more general downside from sunsetting--it increases opportunities for lobbying. Worse, it benefits long-term preparation and strategy, which will favor monied interest groups and lobbyists especially. Which is similar to the downsides of term limits, which effectively shifts power to those behind the scenes--e.g. political operators, party bosses--rather than to the electorate. If you make serving in an office a literal revolving door, you empower those positioned to line people up at the door. Likewise, if you make lawmaking a process of continually rehashing old compromises, you empower those playing the long game.
