Management might not be so dumb. If someone said 2 months and you say 6 months, they might go with the person who said 2 months but will accept 5 months secretly.
The 2 month version could be sold at all, the 6 month one can't, so it's not worth considering its technical merits.
Then the client/stakeholder buys in, the sunk cost, well, sinks in, and things get fixed. Success!
In 6 months you need a better scaling version while the current version is creating cascading database failures; it's got terabytes of denormalized data that is out of sync and a 2nd team can't migrate the data in 12 months.
In 12 months, you find 5 other teams copied the 2 month solution.
In 2 years, you have 0 devs left that can solve the problem and a 1000% grown dev team that is great at the 2 month solution.
You ask the teams why they don't use the scalable solution and they say, "do we have any examples of that, the unscalable way is our convention"
If it’s a conspiracy not everyone is in on it, at least. There’s more an element of believing your own PR in many cases.