Historically, there have been plenty of companies that tried offering terms like "neither party can end employment without significant penalties without a year

Historically, there have been plenty of companies that tried offering terms like "neither party can end employment without significant penalties without a year of notice" – for example, see non-competes in finance, which require the employer to keep paying the employee while they're on leave. Employees in the US tend not to prefer such agreements. It seems like most people prefer job mobility to guaranteed tenure.