That’s way too simplistic. Cancers rarely develop in the actual subcutaneous or intra-abdominal fat tissue which is what obese people have too much of.

Sarcomas comprise a heterogeneous group of rare neoplasms that develop from bone and soft tissue. With an incidence of ~7 per 100,000 people, they account for 1% of adult cancer diagnoses […] Liposarcomas (LSs) are rare mesenchymal soft-tissue sarcomas that are thought to arise from cells in the lipocyte lineages in soft tissues. LSs account for ~13–20% of all soft-tissue sarcomas.

Their organs aren’t any bigger, except for maybe the steatotic liver, so no it is definitively not a case of more tissue to develop cancer in.