What do manufacturers of pharma Testosterone recommend for the injection frequency, every 2 weeks? Clearly that is far from optimal, yet it is what they 'recommend'.
Pharma firms create recommendations not to optimize the drugs' efficacy and safety, but to make taking the drug as convenient as possible for patients, while still getting a satisfactory effect. Why do they do that? Because their incentive is to sell as many products as possible. If patient compliance is unlikely, doctors won't prescribe it.
There must really be solid evidence from RCTs about the superiority of a certain dosing scheme for pharma manufacturers to adopt it. In the case of T3, there is a lack of such evidence. This is also why T3 is very rarely used by doctors to treat hypothyroidism: there are no large, reliable studies showing that it is as effective and safe as T4 therapy.