Bloatware is a term that emphasizes negative connotations of newer computer systems coming from manufacturers with software loaded on them that aren't exactly as efficient as possible. These programs usually use larger amounts of system resources are often times are merely advertisement trade-offs with system manufacturers. A computer company will get paid X amount of dollars to include trial versions of software A, B and C, regardless of the hit in system performance it takes. The company Hewlett-Packard is well known for loading their new systems with unnecessary software packages.
Bloat itself is described as: The tendency to replace efficient and focused applications with less efficient enhanced versions, inefficiencies or unnecessary modules in program design and operation and the incorporation of extended features which will be extraneous or low value for most users but slow down the program overall even if unused. The latter is often attributed to the marketing trade-off mentioned earlier.
In the early 1970s, programmers and developers had very Limited amounts of space to work with, therefore they had to code with every bit and clock cycle accounted for. Today, this practice is reversed. Space and memory are so cheap and plentiful that developers have seen a way to turn this into a marketing feature and are often put as a priority.
Software development tools and approaches often result in changes throughout the program to accommodate each feature, leading to a large scale inclusion of code which affects the main operation of the software, and is required in order to support functions that themselves may be only rarely used. In particular, the advances in resources available has led to tools which allow easiest development of code, with less priority given to end efficiency.
Some of the observed bloat can be attributed simply by the addition of new features and content such as templates or by the use of higher-level programming languages. However, other times it could simply be because the programmer lacked the initiative to clean his code into a more efficient module as space wasn't a concern.
Finally, several conspiracies point towards a collaboration between software and hardware companies to intentionally bloat their software so systems run slower, thereby making the consumer believe they must indeed buy newer hardware to run up to the level of performance they were promised.