text: Title: Heatmap doees not display all entries
  Body: Hi all,
  
  I have an issue with my heatmap.
  I generated a dataframe with 30k columns and here I set some of the values to a non-nan value (2k of them) (some might be double hits but that is beside the point). The values I fill the dataframe with are values between 0-1 to tell the function how to color each sample
  
  When I plot this, I only get a low amount of hits displayed and wondered why this is.
  
  In my real case example what is shown is even less (more rows, less non-nan's) as in this example.
  Am I doing something wrong here?
  
  python=3.12; seaborn=0.12; matplotlib=3.8.2; pandas=2.1.4 (Ubuntu=22.04)
  
  ```
  import seaborn as sns
  import matplotlib.pyplot as plt
  import matplotlib as mpl
  import numpy as np
  import os
  import pandas as pd
      
  new_dict = {}
  for k in ["a", "b", "c", "d"]:
      v = {str(idx): None for idx in range(30000)}
      rand_ints = [np.random.randint(low=0, high=30000) for i in range(2000)]
      for v_hits in rand_ints:
          v[str(v_hits)] = v_hits/30000
      new_dict[k] = v
  
  df_heatmap_hits = pd.DataFrame(new_dict).transpose()
  sns.heatmap(df_heatmap_hits)
  plt.show()
  ```