One reason is that NASCAR has made changes to the cars themselves.

In 2015, NASCAR implemented a new set of rules for the cars, known as the "low downforce" rules package.

This package reduced the amount of downforce on the cars, which is the force that keeps the car on the ground as it speeds around the track.

The idea behind this change was to make the cars more difficult to drive, which would make the races more competitive and exciting for fans.

However, the reduction in downforce also means that the cars are slower.

With less downforce, the cars cannot take corners as quickly, and they cannot accelerate as quickly out of the corners.

This has resulted in slower lap times and overall slower races.

Another reason for the slower NASCAR races is the tracks themselves.

Many of the tracks on the NASCAR circuit are old and worn, and they have not been updated to keep up with advances in technology.

This means that the tracks are not as smooth or as fast as they could be.

Additionally, some of the tracks are simply too short to allow for high speeds.

For example, the Martinsville Speedway, which has been on the NASCAR circuit since 1949, is only 0.526 miles long, which means that the cars cannot reach their top speeds.

Additionally, NASCAR has implemented safety measures over the years to protect drivers.

For example, the use of restrictor plates has been implemented on certain tracks to limit the amount of air and fuel that enters the engine, which reduces the speed of the cars.

This was done in response to several high-speed crashes that occurred in the 1980s and 1990s, which led to several deaths and injuries.

The restrictor plates have been successful in reducing the speed of the cars and making the races safer for drivers.

Another factor that has contributed to slower NASCAR races is the tire compounds used on the cars.

In recent years, NASCAR has mandated that all teams use a single tire supplier for all races.

This means that the tires used on the cars are designed to last longer, which reduces the number of pit stops that teams need to make during the race.

However, the downside to this is that the tires are not as sticky as they used to be, which means that the cars do not have as much grip on the track.

This results in slower lap times and slower overall speeds.

Finally, NASCAR has also made changes to the race formats in recent years.

In 2017, NASCAR announced that it would divide each race into three stages, with points awarded to the top finishers in each stage.

This was done to add more excitement to the races and to encourage drivers to race aggressively throughout the entire race.

However, the downside to this is that the breaks between the stages allow the cars to cool down, which means that they cannot perform at their highest speeds during the entire race.

In conclusion, there are several reasons why NASCAR races have been getting slower over the years.

Changes to the cars, tracks, safety measures, tire compounds, and race formats have all contributed to slower lap times and slower overall speeds.

While some fans may be disappointed with the slower races, it is important to remember that these changes have been made with safety in mind, and that the races are still exciting and entertaining for fans to watch.