Why doesn't NASA, ESA & other space agencies investigate Mars's poles for evidence of past life?

If Mars once had life & it was life as we know it , the only places on current Mars where such life may still exist is at Mars's poles being they are sources of water. I remember hearing that a decently sized lake was discovered under Mars's south pole. It's not impossible that that very subglacial lake may have surviving & thriving Martian microbes?

And regarding Perseverance's samples from Jezero Crater? It'll be the greatest moment of all time if those rock samples have fossil evidence of microbial life as it'd be proof positive that Earth isn't the only world with life. But we won't know anything about those rock samples until 2033 when those samples are returned to Earth for examination.

Well there was the mars polar lander. It crashed. But the areas of most interest are those with evidence of previous liquid water. In terms of past life these might be more interesting.