It may have designed as a stack to better decoding math expressions. Or they may have used stacks because Intel liked stacks at the time.
It's known that the 8087 was designed to attach to either the 8087 or Intel's 32-bit chip the 432. The contemporary rumor is it is in fact the floating point unit FROM the 432, a money-is-no-object project to make the "ultimate" 32-bit chips. The 432 itself had only stack-based registers, had all kinds of weird-length instructions, had to be split across multiple chips, and locked those registers away from programmers who were only allowed a slow high-level language to program it. Only when 432 was clearly failing was also paired to the 8086/88--a chip that itself was a crash project because of delays in the 432. Adding the very different 8087 to the 8088 was described as pairing a race car engine into a poky Volksagen bug.
On the other hand, getting floating point right in the 8087 was absolutely worth the effort. You can see the comparisons in a 1983 issue of Hal's newsletter on the Savage benchmark: http://www.easy68k.com/paulrsm/dg/dg26.htm. Go to "Timing Conclusions" and particularly "Error Conclusions" and beyond.
It's known that the 8087 was designed to attach to either the 8087 or Intel's 32-bit chip the 432. The contemporary rumor is it is in fact the floating point unit FROM the 432, a money-is-no-object project to make the "ultimate" 32-bit chips. The 432 itself had only stack-based registers, had all kinds of weird-length instructions, had to be split across multiple chips, and locked those registers away from programmers who were only allowed a slow high-level language to program it. Only when 432 was clearly failing was also paired to the 8086/88--a chip that itself was a crash project because of delays in the 432. Adding the very different 8087 to the 8088 was described as pairing a race car engine into a poky Volksagen bug.
Rumors mongered in 1982 by Hal Hardenburgh: http://www.easy68k.com/paulrsm/dg/dg06.htm, "Page 4" section.
On the other hand, getting floating point right in the 8087 was absolutely worth the effort. You can see the comparisons in a 1983 issue of Hal's newsletter on the Savage benchmark: http://www.easy68k.com/paulrsm/dg/dg26.htm. Go to "Timing Conclusions" and particularly "Error Conclusions" and beyond.