Simple languages tend to be very unportable. This has been a plague on Scheme since the beginning, and which the R6RS / R7RS standards have tried to rectify (it's debatable how successful this effort has been). This is one way in which simple languages are limited. (The fact that there are many different Scheme standards certainly doesn't help).
Another part is stripping of useful features to ease implementation. The Scheme language is full of uncomfortable, low-level constructs for the sake of simplicity. In contrast, Common Lisp is far from simple but it contains many high-level constructs which are nonetheless simpler to use.
On the contrary. A simple language can be relatively quickly implemented on another system, because there is not much to implement. If we look at how many Schemes there are, implemented for various platforms, and compare that to how many Common Lisps there are, we quickly see that difference. Of course CL is also more geared towards being "the one" language, rather than "make your own version of CL", exactly because of the effort required to do so. In that way one could argue it cannot even get close to the portability of a simpler language.
> Another part is stripping of useful features to ease implementation.
With useful features, you mean things, which reduce work of implementing things? Of course a bigger language will have more stuff built-in – That's in the definition of bigger language. The point is though, that Scheme does enable you to build these things. Once there is a library for it, you can use it just like other in-built things in CL. Whether that always happens to happen (a library existing), is another question. There is nothing in the language, that would prevent you from building that thing though.
> The Scheme language is full of uncomfortable, low-level constructs for the sake of simplicity.
I find them very comfortable. I also find its simplicity refreshing and a pleasure to use. It enables me to gain more understanding of concepts, which I might implement or copy from others.
Another part is stripping of useful features to ease implementation. The Scheme language is full of uncomfortable, low-level constructs for the sake of simplicity. In contrast, Common Lisp is far from simple but it contains many high-level constructs which are nonetheless simpler to use.