As each party, over time, opposes the otherv, the center loses priority. People eventually feel less and less represented by their party of choice but will not change if the change means the only choice they have is that which they have long opposed.

I believe most GOP voters would happily abandon the platform if any reasonable choice were available.

Likewise, Dems have long been frustrated by a party that seems rife with weaponized incompetence.

If a third party were effective at unifying these long opposed factions, it would prioritize current issues that are commonly recognized across the divide.

For example, the Clean Party, who's primary mission is to eliminate corruption from the political process and keep the machine running as intended. Most people agree that corruption has really messed everything up but must accept it as the way of things. The idea of "draining the swamp" was incredibly important to DT's rise, and many have been disappointed.