What can cause the CPU usage drop in the script moviepy FFMPEG

Question

What would cause the exporting rate to drop or cpu usage to drop between these 2 scripts

This one exports with a rate of 15bit/s

clip1 = VideoFileClip("C:/TBD/TBD/#Frikkie/T1234567/Export/01.mp4")
clip2 = VideoFileClip("C:/TBD/TBD/#Frikkie/T1234567/Export/02.mp4")
clip3 = VideoFileClip("C:/TBD/TBD/#Frikkie/T1234567/Export/03.mp4")

final = concatenate([clip1,
                     clip2.crossfadein(1),
                     clip3.crossfadein(1)],
             padding=-1, method="compose")

final.write_videofile('myvideo.mp4')

This one drops down to only 3 bit/s

path = "C:\TBD\TBD\#Frikkie\T1234567\Export"
videolist = []

for clips in glob.glob(os.path.join(path, '**')):
    print(clips)

    if ".mp4" in clips:

        videolist.append(VideoFileClip(clips).crossfadein(1))

print(videolist)
final = concatenate(videolist, padding=-1, method="compose")
final.write_videofile('myvideo.mp4')