From a Curbed.com online article:

When Disney died in 1966, the mansion was still being planned as a walkthrough experience. As imagineer Rolly Crump recalled in a 2005 interview, visitors would be escorted through its rooms by a “ghost host” who would provide a backstory for the house’s mysterious hauntings.

This format would allow for meticulously timed illusions, impossible to pull off with guests moving through the attraction on a track. Crump and fellow designer Yale Gracey devised a series of clever apparitions to enthrall guests throughout the experience. Most of these relied on an old trick used by magicians and hoaxers of the Victorian era.

The Haunted Mansion was never supposed to be a ride.

The iconic Disneyland attraction, which turns 50 today, was first conceived as a walkthrough tour—somewhere between a carnival’s house of horror and a visit to San Jose’s spectacular Winchester Mystery House. Its development took nearly 20 years, and plans for the project changed constantly as designers fought over what park visitors might find within the walls of the neoclassical estate.

To read more click on following link: https://la.curbed.com/2019/8/9/20794585/disneyland-haunted-mansion-ride