Sebastian Vettel has had one of the more illustrious careers in F1. He is on the list of drivers with the most wins in Formula 1, with his four world titles with Red Bull.Everything does come to an end, however, and the same goes with the careers of some of the greatest drivers in F1 history. Vettel, driving for Aston Martin, is closer to the end of his career than many would imagine. In this piece, we look at 3 reasons why the German might retire at the end of this season.Sebastian Vettel's performance levels have dropped significantlyFormula 1@F1Seb's finest performance for @AstonMartinF1, so far Re-live Sebastian Vettel's incredible P2 finish in Baku with fresh insight and behind-the-scenes action The latest Inside Story is available globally for F1 TV subscribers #AzerbaijanGP #F14:36 AM · Jun 16, 20215760338Seb's finest performance for @AstonMartinF1, so far 💪Re-live Sebastian Vettel's incredible P2 finish in Baku with fresh insight and behind-the-scenes action 😍 The latest Inside Story is available globally for F1 TV subscribers 👇#AzerbaijanGP 🇦🇿 #F1Sebastian Vettel's legacy has taken a hit in the last few years as his performances have not been up to the mark. A driver who was almost always considered to be one of the best on the grid has slowly seen himself fall down the pecking order. The rest of the field seems to have been gradually getting the better of him.It all started in 2019 when the four-time world champion was beaten by then team-mate Charles Leclerc in the latter's first year at Ferrari. The dip reached rock bottom in Vettel's last year with the Italian outfit in 2020.Vettel did bounce back a bit in his first year at Aston Martin, but it's hard to call the overall performance vintage Sebastian Vettel. If the German's best days are behind him, then he might not be the best available option for Aston Martin right now.The Aston Martin project might be too long termSebastian Vettel joined Aston Martin with the prospect of growing the team and taking it to a point where it was capable of fighting upfront. The current trajectory for the team, however, does not look promising in that respect. The team still has too many holes to plug, and if one is to expect a turnaround, then it won't be happening soon for the team.The questions therefore arise: Will Vettel, who is not getting any younger right now, be willing to wait that long? Will he even have the motivation to fight in the midfield after fighting at the front for far too long? The answer is most probably no to all these questions, raising the possibility of Vettel leaving the sport at the end of the season.Pierre Gasly is lurking at Alpha TauriPIERRE GASLY 🇫🇷@PierreGASLYP1!! My first victory in F1!!I’m lost for words, still struggling to realise, its just amazing!! Everything was perfect, just missed the tifosis down under the podium. @alphatauri we have done it!! Thanks everyone for all the messages & support!! Today is a day I’ll remember.12:10 PM · Sep 7, 202020282128845P1!! My first victory in F1!!🏆I’m lost for words, still struggling to realise, its just amazing!! Everything was perfect, just missed the tifosis down under the podium. @alphatauri we have done it!! Thanks everyone for all the messages & support!! Today is a day I’ll remember. https://t.co/3eILYSMsIuSebastian Vettel's contract will run out at the end of the season. If his performance is at par with what is expected of him, then he can expect an extension without much of a doubt. This, however, also depends on whether Aston Martin can produce a car that keeps the competitive juices flowing for the German,If either of the two is not the case, we might see the German leaving the sport for good. The added incentive for the Silverstone-based team could be a hungry and talented Pierre Gasly waiting in the wings at Alpha Tauri, desperate for an upgrade. At the end of the season, Aston Martin could very well look at the Frenchman as the future of the team and bring him in to fill Vettel's shoes.