Because it's a v30 feature. Backporting it onto minor update of v28 circumvents Core node runner's ability to choose, by "sneaking it" into what appears to be a maintenance update.
It looks like thin...
... Yeah, but its not a controversial upgrade at all and those transactions are valid. Means those who want to run older nodes can keep up to date on security patches AND remove arbitrary restriction on the fee that are alrewdy on the network.