Is liquid water on Mars such a big leap compared with ice? I thought we have found bacteria or other kinds of life on Mars.

Now it is liquid water.  Is there such a big difference between liquid water and iced water?
We have not found life, bacterial or otherwise, anywhere other than Earth ... yet. I think you mean the difference between liquid water and water ice. This difference relates to the hospitality to life. Life of the type we are used to needs liquid water, even if this is just trapped moisture, unless the life is temporarily in suspended animation. If there was no liquid water on Mars, there would seem to be no possibility of ongoing life there.

It is important to distinguish hospitable conditions from evidence for life. While having a hospitable environment is necessary for life, it is far from proof of life. The big hurdle is starting life, or bringing it from somewhere else.

There are a variety of hospitable environments in the solar system and on exoplanets, such that if certain life from Earth (such as extremophile bacteria) were somehow placed there they could live. But that does not mean there is in fact life there.

Another important point, Mars was way more hospitable early in it's history, with bodies of liquid water. Which is important because even though starting life on Mars under current conditions is unimaginable, early Mars was rather Earthlike and could possibly start, or receive, life.