This is not true, anonymous attributes will be removed when they are not referenced anymore. The capture attribute node can actually completely skip generating the data if it isn’t needed.
In general, anonymous attributes give us quite a few optimization opportunities that we wouldn’t have with named attributes.
But I think the bigger reason to prefer anonymous attributes is that connections are expressed with node links, and you don’t have to use arbitrary (or potentially conflicting) names to reference data. Of course different people will prefer different workflows, but the anonymous workflow is definitely more portable and probably easier to read, especially when we have something like hidden node links.
We’re not considering deprecating anonymous attributes, that was never the idea with adding the named attribute nodes.