Finally, what bloat is today, is necesary tomorrow. Imagine an oracle database on hardware from the seventies. Bloated beyond imagination, dog slow. But since the seventies the amount of data stored in a database has grown tremendiously, to the level where we simply need databases like Oracle or SQL Server to store it.Bloat isn't an absolute metric. Bloat is the ratio of the memory and execution footprint of a program to the useful work it gets done. A program which does the same amount or less useful work than another program, and which is twice the size in core and uses twice as much CPU time as the more efficient program, is referred to as bloated. It would be illogical to refer to a database server such as Oracle simply as bloated, unless it were possible to point out a competing database server which is equally as useful and which has a smaller footprint, either due to careful coding or to better algorithms. In the case of Oracle, this might be true. But just because it doesn't produce useful work on the hardware of 30 years ago doesn't mean it isn't a well engineered piece of software.
A better label to use would be "complex". To respond to your argument that the only obstacles to db-fs are ignorance and blind conservatism, complex software is undesirable. It increases costs in terms of man hours to maintain it, it increases QA overhead, and it increases support calls from users who came to depend on a feature which was included for completeness, but was never audited for correctness or robustness. People don't code complex software unless they are paid to do it (and usually when a manager is making the technical decisions). This is the reason most open source/free software tools seem to follow the Unix philosophy; simple tools which do one task and do it well, but are yet flexible enough to build into more complex systems. A monolithic database filesystem does not appeal to the sort of psyche which produces open source code for that reason: Complexity doesn't make a programmer's job fun. In order to produce large amounts of code at a low cost as in the open source/free software world, the people behind the engineering of the software need to be having fun, and a complex database filesystem is a rather good example of something which is _not_ fun to produce and therefore unappealing to the hacker sort.