2011 also only had one previous winner at the start. Same in 2012. In 2002 Armstrong was the only previous winner. No previous winner was at the start in 1999. It really isn't that unusual.
In 2002 and 2011 that winner had won multiple editions, though, which was what I commented on.
2020: 1 edition won by riders on start list
2019: 2
2018: 5
2017: 6
2016: 6
2015: 5
2014: 4
2013: 4
2012: 1
2011: 3
2010: 10
2009: 9
2008: 0
2007: 0
2006: 0
2005: 7
2004: 6
2003: 5
2002: 3
2001: 3
2000: 3
1999: 0
1998: 2
1997: 1
1996: 5
1995: 4
1994: 6
1993: 6
1992: 8
And there I was born, so things before that are unimportant (or I just didn't want to spend more time on this )