TPM is not HSM, not enclave, and it does not allow running arbitrary computation. TPM is a specification of a secure element, that provides some cryptographic primitives, secure storage, signing mechanism (endorsement key), and a few more. Since it is available since very early boot stage it is used for storing and signing integrity measurements.
HSM or TPM never release the signing key as authors writes. DICE does not release the initial seed used to derive the inital hash/key.
DICE addresses different market. It was designed by the same organization that designed TPM but addresses IoT devices. Microsoft extended the spec so that one gets chain of signed measurements instead of an aggregated hash as an attestation proof (at a high level).
DICE gets more popular in TEE designs because one does not have to rely on an external chip vulnerable to physical attacks. However, it is the same set of features needed for DICE and TPM to enable attestation. TPM offers additional features, like mono tonic counters, secure storage, sealing, etc, that can be used for other use cases.
Finally, TPM became a standard and has been implemented as part of complex processor’s firmware (Intel PTT), discrete TPM (what the author of the article is familiar with), software TPMs enabling attestation for VMs and recently used also for confidential computing VMs (check Intel TDX). Linux kernel supports runtime integrity measurements with IMA security subsystem that relies on TPM protocol for attestation.