Since most stock ownership has become a digital ledger, there are incentives for consolidation toward central custodianship for clearing and settling of trades.

The DTC is part of the subsidiary family of the DTCC, which also operates the NSCC. The NSCC handles security clearing for almost all equities trading in the US (all transaction systems basically report here at the end of their reporting chain).

This basically allows the NSCC to simply update the ownership accounting of a number of shares, as opposed to hunting down the physical stock certificates, validating their authenticity, and then handling the transfer.

This has ultimately greatly reduced the settlement window (from Trade date + however long it takes to find the certificates, to, as of a month or two ago T + 2 days), which allows firms to free up capital (the cash doesn't exist until the trade settles) to commit to other endeavors.

A shorter settlement window (and the consolidation down to a single system), also reduce overall counterparty risk, as once the trade is settled you don't necessarily have to be concerned with the financial well being of the firm you did the trade with.