Signing a good and reliable goalkeeper is not that easy again in football, so you wouldn't put all the blame on Chelsea head coach for not signing a reliable goalkeeper for Chelsea when the transfer window was open. Maybe when Maresca took over as Chelsea head coach, he didn't see the goalkeeper as a major problem for Chelsea, and that could be the reason he didn't bother to sign a new goalkeeper for Chelsea. Since Chelsea is in the rebuilding process, goalkeepers will find it difficult to perform well at Chelsea because they won't have good squad depth, and their opponents will penetrate their defense very often, which will give any Chelsea goalkeeper a difficult time to perform as expected..
I don't think so. If a club has a good strategic transfer planning then finding the right players that will align with the coaches tactical vision wouldn't be a problem. And for Chelsea they have failed in improving their overall performance notably the goalkeeping department. What do you even expect from a owner who doesn't have the experience in English football? Even though Chelsea are in the rebuilding process, saying that goalkeepers would find it difficult to perform well is just an excuse to justify their mistakes. They really need to put an end to their goal keeping issues quickly if they aim at competing constantly at the highest level.