>>30329"Ongoing drills in completed Vaults slowly created a cry wolf effect: Turnouts for the drills fell as the years went on, limiting the Vaults' future role in ensuring the survival of humanity.[Non-game 10] However, even if they didn't, the shadow government decided against Vaults being shelters for preserving humanity.[Non-game 11] After establishing control over Project Safehouse, they subverted it to their own ends. Rather than act to save humanity, Vaults were built to test their population as part of the Societal Preservation Program.[30] Only 17 of the Vaults were designed to work properly as control Vaults.[31] The 105 other Vaults featured a variety of scenarios, ranging from annoying to downright lethal, to gauge how humans acted in these scenarios for their own, nefarious purposes.[Non-game 12] Some were not provided with enough food synthesizer for their population, others had only men in them, or were designed to open prematurely. The purpose of this experiment was to gather data for the Enclave's own projects, the exact purpose of which is unclear.[32]"
Tldr: Vault Tec was taken over by the enclave who only intended to use the vaults for research purposes, they didn't care about them beyond that. Vault Tec was just a corrupt corporation that wanted to make money out of making vaults, they either didn't think the war would actually happen or didn't really care and just wanted to make money.