It is rumoured that Air France-KLM, the team's title sponsor, required in their contract with the team that at least one driver would be Dutch or French. Replacing Mattson with Lindsey would violate this requirement.
Lindsey: "I'm very happy to make my debut with KLM Team 23 this weekend. I'm really looking forward to driving a F1FVGPC car again after my test in Jerez, because it's so much fun!"
For now, it is unsure how the new driver line-up will affect the team's sponsorship. According to rumours, Air France-KLM could withdraw their sponsorship during the season.