The early versions of Microsoft BASIC required 4KB of ROM, and many versions existed in the 8KB and 16KB size. But Microsoft's IBM BASIC (known as "Cassette BASIC") for the original IBM PC (Model 5150) required 32KB. This seems odd to me given competitors like:

1. 8KB CBM BASIC v2.0 in the Commodore 64, which had all the essential disk file functions (but no graphics).
2. 16KB CBM BASIC v7.0 in the Commodore 128, which had many enhanced features plus graphics.
3. 16KB BBC BASIC which perhaps had the broadest features of any comparable BASIC and even out-performed IBM BASIC running on the faster PC.

Why was the IBM BASIC so huge (relatively speaking) at 32 KB?

The early versions of Microsoft BASIC required 4KB of ROM, and many versions existed in the 8KB and 16KB size. But Microsoft's IBM BASIC (known as "Cassette BASIC") for the original IBM PC (Model 5150) required 32KB. This seems odd to me given competitors like:

1. 8KB CBM BASIC v2.0 in the Commodore 64, which had all the essential disk file functions (but no graphics).
2. 16KB CBM BASIC v7.0 in the Commodore 128, which had many enhanced features plus graphics.
3. 16KB BBC BASIC which perhaps had the broadest features of any comparable BASIC and even out-performed IBM BASIC running on the faster PC.

Why was the IBM BASIC so huge (relatively speaking) at 32 KB?

Note/Update: The total amount of ROM in the original IBM PC is 40KB. The additional 8KB being for the PC BIOS. It came on 5x8KB ROM chips.