This does not shock me. In the corporate world, plans are not there to be adhered to, but only to give upper management a feeling of having tightened the rope for those pesky engineers who wanted to work at a lazy pace. Such feeling usually vanishes as soon as reality kicks in.
If a project is projected to be finished in 6 months, the current manager will still be there, and the success or failure will reflect on their record. It can only go wrong and reflect badly on them.
If a project will take 3 years, the manager can already collect their points for initiating a project with an incredible business case and innovative approach, leave after 18 months, and after a further six month, the new manager can say 'wow, my predecessor left a big mess, I'll clean it up/kill it'.