This is a good video of why 2004 hopes are little far fetched. These are the reasons he gives:
1. There is no reasonable study that has shown that lower turnout hurts the BJP. Some studies have shown that sometimes lower turnout could benefit the BJP as well
2. NDA is far stronger in UP/Bihar than it was in 2004. In 2004 the NDA only won 22 seats in both states while in 2019 that number was 101 and they got over a 50% vote share as well
3. Ram Mandir helps among Northern voters where the BJP has a lot of seats
4. There is no equivalent to Sonia Gandhi in 2004 for the opposition and the lack of one major leader gives the BJP the advantage on the issue of "strong stable leadership"
5. The BJP has far more momentum in the south today than it did back in 2004 and far more seats are winnable for them there then there was back then.