How to explain the high swampiness of Western Siberia?

It is known that Western Siberia is one of the most swampy areas of the Earth. Several natural factors have contributed to this.

1) Relatively flat terrain. Absolutely flat areas on Earth do not exist, however, within Western Siberia there is a very small elevation difference, therefore, it is said about the plane of this plain.

2) Try pouring a glass of water onto the table. A small puddle forms on the surface of the table. If you tilt the tabletop, water will immediately spill onto the floor. There is no such slope of the surface in Western Siberia. Therefore, the surface runoff is hampered, the rivers of the Ob basin have low flow rates. Everything is aggravated in the spring. The Ob flows from south to north. When the flood begins in the upper reaches of the river, the lower reaches of the river are still frozen in ice. Jams form, the river overflows and floods huge areas. Spring floods on the Ob are long lasting.

3) Peat deposits, like a sponge, absorb water during floods and retain this moisture for a long time.