It's nostalgia, for the most part, and I say this as someone who loved, and still love, everything about it. But I don't use it anymore and wouldn't recommend it to anyone.

Everything started with Borland's Turbo Pascal back in the 1980s. It was an IDE with a lightning fast compiler and built in debugger. Extremely slick, and it was so fast that there was hardly any time to wait for a build. It was extremely small and produced fast programs. And it was very affordable. Everyone loved TP.

As a language, TP implemented its own dialect of Pascal that turned what was originally a somewhat clunky, limited teaching language into a "real" language; for example, TP had assembly language built in, so you could write hand-optimized code for things like low level graphics. Eventually TP added object oriented programming that rivaled other languages like C++. This was before modern languages like Java and C#.

Borland released a Windows version, but it was basically the same thing but with a GUI. To write GUI apps you had to use a library called OWL and basically define the UI in code, by creating objects like buttons and fields. It was quite good, and played to TP's strengths, but real game changer was Delphi, which ended up becoming TP's successor. It was an IDE which supported everything TP did, but reoriented it around designing Windows GUI apps visually.

In Delphi, you built your UI drawing components and dragging them around, laying out each window and attaching behavior such as click handlers. Some components represented non-visual components such as database connections. The beauty was what they called "two-way editing". Changing the GUI updated the code, and vice versa. A key concept was that the components you were editing were "live"; they weren't mocked-up versions of anything, but actually ran your code right inside the IDE. Programming in Delphi felt more "live" than with other stacks (like Visual Studio) because the whole design-build-test lifecycle was so fast.

Many people considered Delphi to be a more advanced, "grown up" alternative to Visual Basic, which emerged around the same time and was in many ways quite similar, though Delphi was arguably much better. And indeed, since that time, nothing has really managed to match Delphi's ease of development; not VB, not Interface Builder, not whatever Sun was doing with Java and Swing at the time. Tons of people were extremely productive making GUI apps in Delphi, and as with TP, there was a strong developer culture around it, especially in Europe.

In both the case of TP and Delphi, the language was probably the least interesting thing about it. Pascal has always been a little verbose and clunky, and people succeeded despite of it. People who didn't grow up with TP/Delphi who look at it today will almost certainly wrinkle their noses at the sight of this language, and they'd be sort of right. It was never a great language. But it was an incredibly productive one. The speed, elegance, and "vertical integration" of these IDEs were significant force multipliers.

Delphi started to lose for many reasons: Borland's mismanagement, Microsoft playing hardball with them, the emergence of Java, the emergence of the web, the steadily increasing dominance of C++ (and rejection of niche languages), and so on. The fact that ObjectPascal was a niche language meant that Borland was always the underdog and suffered from poor interoperability with standard C/C++ tools; Delphi didn't consume C header files, so a new C library (DirectX or MAPI or TAPI or whatever) always required manually writing glue code to talk to it. Delphi fans were loyal, but they were always second-class citizens on Windows. (Even though Borland eventually launched a C++ version of Delphi, it never really caught on.) The world's focus away from desktop apps to web apps was just one more thing Delphi couldn't keep up with. And I say that as someone who wrote Microsoft IIS web servers in Delphi for a long time and built products that required interfacing with C libraries.

If Borland had been able to keep their eye on the core product and stay true to their development tool company roots, they might have survived to this day. But they didn't. TP and Delphi are now relics of a bygone era, much like the Amiga, the Acorn, the Nokia Communicator, and other examples of "superior tech that never took over the world." But like those other examples, the superiority is local to that era. You wouldn't bother using an Amiga for your main work today, and I wouldn't use Delphi. ObjectPascal was neat, but today it's antiquated compared to languages like C#, Rust, and Go. Delphi was always Windows-only, and these days cross-platform support is more important.

I should add that I've never used Lazarus. It looks like a Delphi clone, and it's probably quite nice.