A small team is forced to design small, for example original ARM designers

The success of the ARM processor vs. Intel is obvious in the mobile market.  Going back to the history of the ARM it is interesting to note the small UK design team vs. the US.

One of the reasons the ARM was designed as a small-scale processor was that the resources to design it were not sufficient to allow the creation of a large and complex device. While this is now presented as (and genuinely is) a technical plus for the ARM processor core, it began as a necessity for a processor designed by a team of talented but inexperienced designers (outside of university projects, most team members were programmers and board-level circuit designers) using new tools, some of which were far from state-of-the-art. With these restrictions on design and testing, it is hardly a surprise that a small device was developed.

While the ARM was developed as a custom device for a highly specific purpose, the team designing it felt that the best way to produce a good custom chip was to produce a chip with good all-round performance.

In the US the RISC teams at Intel, AMD, Sun and MIPS.

For example, Sun developed the SPARC RISC chip and architecture for its own computer workstations, while notable RISC processors from established chip producers include Intel's i860 graphics processor and AMD's 29000, which has mainly been used as a graphics accelerator or in printers. However, both Sun's and MIPS' efforts were based on earlier research efforts at Stanford and Berkeley universities respectively, while Acorn's project was effectively begun from scratch, although reports on the Berkeley and Stanford research were read by the Acorn team and were part of the inspiration behind designing a RISC processor.

The ARM team also was a team focused on price/performance.

The ARM processor has always differed from other commercially available RISC processors in that it is intended to meet a price/performance ratio rather than to be the most powerful processor available. Acorn's computers have always been aimed at the middle of the market, so the processor designed to power them was too. ARM processors are not the most powerful, but offer an extremely good price/performance ratio compared to other processors, at about a dollar per million instructions per second (MIPS) in the case of ARM6.

High performance for low power consumption
A further advantage of the small size of ARM devices is that they do not consume as much power as other, larger processors.

This has proved a critical key to the success of ARM processors. Unlike many other processor designs, the ARM was easily re-implemented in static form rather than the usual dynamic CMOS. This, along with the small die size, reduced power consumption, making ARM processors ideally suited for power consumption-critical products such as portable computers. Furthermore, it allows the clock to be stopped, a useful powersaver in portable designs.

Think about this when picking vendors.  Sometimes the biggest is not the best as they have the resources to create the most complex designs and to market it.