Why are the lanthanides and actinides moved out of numerical order and placed at the bottom of the periodic table?
They aren't always, but for most periodic tables, the width would be very long, and it wouldn't fit very well on an eight by eleven piece of paper.
Look at the expanded form on the bottom:
http://www.theschemata.com/conventional_periodic_table.html
The reason the lanthanides and actinides are moved out of numerical order and placed at the bottom of the periodic table is mainly due to space limitations. If all the elements were placed in their exact numerical order, the periodic table would become too wide to fit on a standard-sized piece of paper.
To accommodate this limitation, the lanthanides (elements with atomic numbers 57-71) and actinides (elements with atomic numbers 89-103) are placed at the bottom of the periodic table in a separate section. This compact arrangement allows for a more practical and organized representation of the elements.
The link you provided shows an expanded form of the periodic table, where the lanthanides and actinides are represented separately at the bottom. In this arrangement, the main body of the periodic table is compressed, making it more convenient for printing or displaying on standard-sized formats.