I've always thought this was a clever strategy, but apparently enough people live in their own social bubbles that many progressive types don't realise how unprogressive a lot of older, rural voters are (and you could argue they've been misled by their news providers into positions that are contrary to their own values and desires) and can't understand why compromise is necessasary to actually win elections.
Some have argued that this is bad because you need to inspire people, like Obama did, but Obama is another triangulator, so I'm not sure how that makes sense.