Reading the history of FPC again and its struggles to be TP and Delphi compatible, after some 5 months effectively working on the SharpBASIC compiler (SBC), I realize how constraining it must be to model a new compiler after an existing language
Well, if you phrase it as "struggles", the mind seems to be already made up before you get to the end of the sentence :-)
I think it is more a difference in goals. Making a widely used suitable for production compiler is simply hard and iterative. There is also a significant difference in general between a one person team, and a multi person team. With multiple people there are also multiple opinions, directions etc.
On the other hand, compatibility also provides an Occam's razor to test random ideas and alternate directions with. Often it is also very clear which feature to tackle next (from the compatibility list) and that is very rewarding since that often makes a whole new class of applications and reusing existing code possible. I can still remember how I excited I felt in the beta period before 2.0 when more and more Delphi code ran without significant modifications
Specially in the early days this keeps language experimentation and the associated discussions to a minimum, and keep your focus on a certain target (like self-compiling/bootstrapping the compiler)
Honestly, I admire the FPC and also FBC (FreeBASIC) developers for honouring the restrictions/limitations and also the ambiguities of the original language for maximum compatibility. It certainly wouldn't be my cup of tea! I say this as a frequent FPC and FBC user; even a trivial thing such as declaring and initializing multiple variables can be hard/impossible to implement:
If such micro syntax is the biggest problem in a language, you'd be very happy. Keep in mind that the Pascal parsing model was ingrained into the fabric of the project. Problems with foreign language constructs not matching the model might have been considered a small or even negligible sacrifice.
Anyway don't fall for the micro syntax trap, it takes more to make a good language than simply implementing a superset of all shorthands of all languages.
In the end what attracts users is visible ability/proof to complete certain tasks, like sizeable programs in the project's target domain. It is not simply a matter of bullet lists of micro syntax comparisons.