Well when you look at how teams generally develop this area, you notice they don't usually change it too oftrn, since it's very important for overall flow structures. You may see one or two teams doing one (small) change of side pod intake design per year, mostly because its either a massive gain or the, made a massive screw up in thr beggining. Mercedes did it in Austria this year for a massive gain for the rest of the year.
On Ferrari, this area seems particularly well developed with clear design goals very visible. Being such, improving it might hurt some of those original goals and/or hurt further development potential for some other areas.
What I'm very intersted in, is why barge board updates are so scarce. There are two possibilities - either they are very close to development potential (hardly) or they are reluctant to introduce new parts that would improve downforce potential but at the great cost of drag. In my view, Red Bull has too many surfaces in this area causing substantial amount of drag for downforce they gain. Red Bull had 3-4 updates in this area since roll-out, while Mercedes and Ferrari each had only one.
Also, it's good to remember that teams learned about 2019 changes very early this season, so they probably started splitting resources between 2018 and 2019 cars at that time. This would hinder any development that doesn't benefit 2018 as much as other areas do (since 2019 cars will be so different, there aren't many parts you can translate to them) and you still have to work on low-drag configuration for Spa and Monza.