The time and effort to get DMARC enforced varies for each business. For some, it may have already been set up by your hosting provider. For other businesses, with just a single sending domain, it could be simple – just add the sending domains to SPF, set up DKIM, create a DMARC record and enforce it.
In the case of larger companies with many internal email sending solutions, identifying and building allow-list servers to put into SPF record can require a lot of effort. Some large institutions employ DMARC specialists for DMARC at enforcement and analysis or management of DNS.