My impression is that construction in 2020 isn't so fundamentally different from construction in 1920 that it would need much unique language per project. The big changes seem to be in quality of material and what gets run through and around the material. Meanwhile, we barely had computers 75 years ago and the whole thing flips on its head every 5-10 years.

Construction is pretty different now. Supply chains are much more complicated and can be multi national even for a domestic house whereas in 1920, you would probably be able to source all the materials for a house from within 20 miles. Legislation, liability and insurance are more complicated. The standard contracts are typically updated every 5 years or so to take account of this. As a result the JCT standard building contract is 120 pages long now compared to about 10 pages in the 1960's.

but the end product is basically the same whereas in computers the end product is quite different. There was no software as a service (at least not like there is now) 10-15 years ago.

The standard contracts don't specify what you will provide, they specify how much it will cost and when it will be provided. Exactly what will be provided is different each time and is generally covered by a written specification and a set of drawings, which are referred to in the contract and are part of the agreement, but they don't form part of the standard text. The building contract itself is an agreement for managing the process for things like changes to specification, the finish date and the process for paying for completed work, rejecting poor quality work or for defining poorly specified work after the contract is in progress. It sets out who has to pay the costs of changes depending on who has caused the changes and pre agrees some of the contractor's management costs.

I imagine all these things are common to software projects?

The basic project management procedures specified in the contract could probably be adapted to procure a software project. But the reason you couldn't just use a building contract for software project is because it also deals with various ancillary things like how the copyright in the design is licensed to the contractor, who is responsible for complying with Site Health and Safety legislation, various construction industry specific dispute resolution procedures required by law to be agreed in the contract, consumer rights law, housing grants and regeneration act, contracts (rights of third parties) act. GDPR, blah blah blah. The legislation is the stuff that is constantly changing.

This exists in Chicago, San Francisco and probably a host of other markets , for apartment leasing. It's actually really helpful for both the tenant and the landlord. Goes a long way to reducing uncertainty, addressing the maze of regulations, and closing loopholes.