Weight is also given to the magnitude of the game and the fact that it was a gutsy buzzer beater win. I can't think of a bigger moment in women's basketball in the last 10-15 years. The streak definitely plays a part in its significance, but even if you just look at this year's team, they were 36-0 and had waltzed through the most brutal schedule in the country with Geno at the helm. No one thought Mississippi State had a chance. Go look at the prediction thread and you'll see that.
On a different argument, I also think it's a product of how far ahead of everyone else people thought UCONN was in 2017, and how little parity the game has seen over the last 20ish years. Since 1995, Tennessee or Connecticut has won 16 of 22 championships. Connecticut had lost 1 game in 4 years. They've also made 10 straight Final Fours and had won 6 of the last 8 championships. 4 of those were undefeated seasons.
Even in an off year, they were undefeated through 36 games and looked unbeatable most of the 2nd part of the season. They played one of the toughest non-conference schedules in the country and had an average MOV of 33 points. In the regionals they won by 15 against UCLA and fans were disappointed with the performance. Can you think of a men's game where that has ever happened in the Sweet 16? 2 nights later they rebound and win by 38 in the Elite 8.
It's the biggest upset I've ever seen in women's basketball. I thought Mississippi State had zero chance to compete in this game, let alone win the game. UCONN has been a machine under Geno and appeared to be so far ahead of anyone else in women's basketball. Louisville/Baylor is second to me because I didn't think Baylor was as good as this UCONN team was. I never expected an undefeated dominant UCONN team led by Geno to lose in the Final Four to a team like Mississippi State. Baylor was also up and down that year with the Stanford loss, a close win at UCONN, and just an 8 point win in the Big 12 tournament. Many thought it would be an epic battle against UCONN if they met in the title game. I thought Baylor was a Final Four lock, and it was a mind blowing upset to Louisville, but it didn't shock me as this one did considering the level of excellence Geno and Connecticut have maintained over the last 22 years.