The adventure of writing a custom DBMS, game engine, or other complex and advanced software classes can be justified by 1) knowing that no existing solution is adequate but 2) it is possible to write something suitable and 3) it will be useful enough to justify the cost.
For example, to insist on the example of Tigerbeetle, 1) no current popular or specialized DBMS is particularly optimized for ledger use, 2) but suitable techniques are well understood; I'm not sure how often 3) it will be preferred to a more general purpose DBMS.
For example, to insist on the example of Tigerbeetle, 1) no current popular or specialized DBMS is particularly optimized for ledger use, 2) but suitable techniques are well understood; I'm not sure how often 3) it will be preferred to a more general purpose DBMS.