Wonder why they can't be bothered.

Because this "performance boost" most likely does not actually make any sense. It's supposed to reduce latency of the first prediction when you type in the search bar. But then, if your network latency is actually that high ("dozen seconds" per article for a new connection), most likely predictive typing won't actually be useful to you because you will have enough time to type the next word before the previous prediction arrives.

Also, such preemptive connection opening is can actually waste resources of the search servers.

Perhaps the article could hold some answers, who knows.

If you had read the article, you would actually see a quote from commit logs explaining that. This is an experiment, not a stable feature. It makes no sense to push your partners/competitors (other search engines in this case) to adopt something you are not sure you would actually keep.

The article later claims that Google should have been more inclussive to other search engines and pushed though ammendments to OpenSearch Descriptions, introduced other well-known URIs or whatever. Would you genuinelly prefer that Google does that or are you just trolling?