Why is my basement floor sinking

Probably because the moisture in the concrete allows bacteria to thrive.
Seal it ,after cleaning

If you meant stinking, then I agree with Nwptsailor.

If you meant sinking, then you may have a slab-jacking job coming up depending on how much sinking is occurring. This depends on how the floor and perimeter foundation footing was formed and poured. Usually if this is a monolithic pour, sinking would not be noticeable for a few years until the siding starts cracking and warping on the outside.

If this is a stemwall foundation with a later poured interior slab in the basement, then settling is occurring due to the lack of a perimeter footing ledge or rebar doweling was not installed. This last choice may not affect roof line or eave levels but if there is a support column in the center, that may be an issue. Usually this type of settling can be detrimental to the overall second story or above load bearing wall structure. Settling can be attributed to moisture saturation of a poorly compacted crushed rock bed under the slab pour and lack of a footing under bearing column supports. Cracks are indicative of some of the problem but may not exist if the slab had good mesh reinforcement during the concrete pour. Keep an eye on where the original flatwork surface abuts the original stemwall that lacks a footing ledge to support the slab perimeter. That is your main guide as to how much the floor is settled. Slab-jacking is a specialty trade not found easily. The cement contractors in your area can refer you to these guys. Rather than explain what they do, its best you hear it from them. Good luck. nmwirez