XGBoost - feature importance just depends on the location of the feature in the data
You can use this chunk of code to plot the feature importance of your data. It is also possible that your data is columned with decreasing importance.
from xgboost import XGBClassifier
from xgboost import plot_importance
from matplotlib import pyplot
# load data
X = 
y = 
model = XGBClassifier()
model.fit(X, y)
plot_importance(model)
pyplot.show()