They’re all late because customers are fools and salespeople are liars.
Customer: “how long will it take (and therefore cost)?”
Three vendors: “less than [the other 2 vendors].”
...iterate until “cheapest” solution is reached ... meanwhile the technical staff at the vendors are losing their minds at the sales team, telling them that what they’re specifying is impossible...
Customer, to vendor [cheapest]: “Here’s a contract. We look forward to this project being delivered on time and on budget!”