Of course they are not trying to save money, they just don’t want us fans to recognize them, because we all know that there is a huge difference between celebrities wearing makeup and without makeup. It can be said that when you see celebrities without makeup, you can't recognize them at all, so they take advantage of this situation to live like normal people after taking off their makeup.
But we can’t overthrow everyone with one stroke, because some celebrities are indeed not very different between their bare makeup and makeup. The reason why they wear so simple and plain clothes is of course just because they wear them when acting. Their clothes are grand enough, so they want to try a simple style, which is also possible. After all, celebrities are also ordinary people, and they like different things, so it is not necessarily true that some celebrities like this simple style, right?
But I think it is safer for them to dress like this. If they dress too grandly, it will not only attract the attention of others, but also pose a threat to their own safety, because you cannot dress 24 hours a day. With bodyguards following you, you are a normal person and you have to live a normal life. If you live in scenes like those in TV dramas all day long, you will soon collapse. This is why so many celebrities suffer from depression. After all, the profession of celebrity is not that easy.
Besides, celebrities earn much more money than ordinary people, so why should they dress up simply to save a little money? So it seems more likely that they either like this style or are thinking about their own safety.