Saints Row was in kind of a good position to be rebooted. Saints Row 4 saw the destruction of Earth, and the death of the last remaining villain. They could have continued their adventures into space, but at some point we're not really doing Saints Row, anymore.
I think the real problem is that they kind of created 2 kinds of Saints Row. Saints Row 1 and 2 were mostly serious with some mild comedic elements, while Saints Row the Third and Saints Row 4 were entirely comedy. The fans of 1 and 2 didn't like the comedy, but the fans of 3 and 4 were able to enjoy the whole series. Saints Row the Third attracted new audiences, while also picking up fans from Saints Row 1 and 2, before they realized how different it was. Now, Volition could have returned to the serious formula of the first two games when they rebooted, but they'd lose their new audience. The gamble they made was to stick with the comedy formula from 3 and 4, and try to hold onto the newer audience. Unfortunately, because they updated their subject matter for the early 2020s, instead of what was kitsch in the early 2010s when SRTT succeeded, that newer audience failed to turn out. The audience of Saints Row is jaded of "woke politics" and didn't want that in their game. A big problem is that people saw a young black woman in skinny jeans with the sides of her head shaved, and assumed that the game was going to be preachy on "woke" subjects, when the reality is that the game lightly parodies that topic.
They had a real shot at success. They took their time, they made a big game, but in the end they misjudged their audience, and now the price is paid.