[Python] Why are the subplots in the subfigures getting smaller?

I am using gridspec within a subfigure. For some reason matshow plots are getting smaller and smaller.

import numpy as np
import matplotlib.pyplot as plt

mask = np.array([
[ 1, 0, 1, 0, 1],
[ 1, 1, 1, 1, 1],
[ 0, 0, 0, 0, 0],
[ 1, 1, 1, 1, 1],
[ 1, 1, 1, 1, 0]
])

fig = plt.figure(figsize = (12,16), layout = "constrained")
figures = fig.subfigures(4, 2)
figures = figures.reshape(-1)
x = np.linspace(0, 1, 100)
y = x**(0.5)

for f in figures:
spec = f.add_gridspec(3, 2)
for i in range(3):
image_axis = f.add_subplot(spec[i, 0])
image_axis.matshow(mask, cmap = 'grey')
plot_axis = f.add_subplot(spec[:,1])
plot_axis.plot(x, y)

plt.savefig('test.png')




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