First, the convention itself is no longer a deliberative body making decisions about candidates and positions. All of that has been settled before the convention, which is no more than a made-for-TV event meant to sell the party's line of products. This is equally true for both major parties. (The minor parties are another story.)
Platforms do not make for good TV. They must be read. No one has yet devised a platform video, or a platform song. Rap would seem to offer an intriguing possibility. But so far, at least, neither party has gone that route.
Lost in this post-modern, media-centric world, the platform committee is generally at the service of the nominee, who may dictate its language so as to fit his or her views. More often, however, the platform is used as a pressure valve for activists within the party's base. These are the people who are rarely satisfied with the nominee's commitment to party catechism (or with the nominee, for that matter).
And that is the other reason platforms have become too hot to handle: The party catechisms keep getting more orthodox. Rather than seek language that brings together the various wings of the party, the contemporary platformers are eager to please those they agree with themselves.
Gone are the days when moderate and even liberal Republicans showed up alongside conservatives and proudly claimed those labels. Gone, too, are the days when Southern Democrats and others called themselves conservatives and seriously contested the party's platform — or its direction.