But web exists on mobile and desktop. It's been easy for a long time to deploy the same stuff to mobile web and desktop web. What hasn't been easy is designing good experiences for the same application across dramatically different contexts. What hasn't been easy is optimizing the same code for dramatically different contexts. I'd argue neither of those has changed much.
In fact, I'd argue that some things devs love about modern development have made those harder.
Obviously there are some specific stand-out projects directly addressing write-once, but have they helped with those two or hidden them under the rug? (Probably varies.)
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