Well the real question might be what is Arietta waiting for?
It doesn't really bother me if they don't spend money, so long as some of it is being spent on other things, and, when necessary, can legitimately be used in the future (it's not true that it all has to be spent this year - if they are really going to sign Machado to a $300 million deal that MLBAM money could certainly go to that, and once they do end up with a much bigger payroll it might still be a while before the profits go back to winning levels).
As the article notes the young pitchers aren't so good that anyone is really being blocked (which is otherwise the reason why they aren't spending more on positions players or a third reliever) but there is still legitimate reason to wonder how much better Arrieta will make the club, and especially what he'll provide in 2019 and 2020.
The article also suggest they sign both Arrieta and Lynn, but to me if you do that you may as well also get Moustakas (though he's not Klentak's type of player and you have all those extra IF options) and maybe a veteran catcher.
I still think they are going to sign someone, but if they don't, it's a strong indication that they still aren't sure what they have - that as many as five of the eight position player spots (LF, RF, C, SS, 3B) are not yet ready to be the core of a playoff-caliber team.