Because it’s asymmetrical.
You should read about the UASF during the block size war. The network complied with the UASF with 15% of the nodes signaling for it.
You are going to argue for the spam chain if a major chain split happens? Good luck explaining why it’s good for Bitcoin to publish CSAM to the public shareholders of foundry and Mara.
Ironically, the centralization and corporate structure of major mining pools today make the soft fork easier to implement.