Through hole parts are often cylindrical. Hence applying stripes is simple in production. Resistors may have five stripes, tolerance, 3 significant digits, and order of magnitude. That is a lot of information to write, "22811" 22.8ohm 1%? In san-serif font what is 88818? It would be possible to read 1, 2 or 5, 6 or 9, and 8 rotated, i.e. upside down, and be confused.
As pointed out by JRE, a letter in the text is used to help ensure the text is the correct way round, e.g. 22K8.
However, while colour blindness is a problem for stripes, dyslexia is for text. I know of people who would write 'k' backwards without noticing.
Edit: There are many written languages which do not use the Arabic digits (in fact, Arabic digits is a misnomer, because the Arabic digits are different shape or value to commonly recognised digits in 'the west'). So printing digits isn't automatically better than a level of indirection via colour which is language independent.
One pretty thing about 7 of the resistor colour codes is it is in the same sequence as the colours of the rainbow (in some cultures), so many people learn that part of the sequence as children.
The through hole cylindrical part could have its wires bent in any direction, and coloured stripes are still legible from any direction.
If written text is applied in only one location, the part value may be obscured or invisible when it is in circuit. That would be a disaster for repair and inspection.
Hence, written text will have to be applied on all sides in order to be legible, which may well be more difficult and hence expensive to produce, and still awkward to read. Stripes don't suffer from this orientation problem. Stripes are simple to use.
Manufacturers have already invested in machinery to product components with colour stripes.
Where is the competitive advantage? There needs to be 'new' money to fund the change over to printed numbers, or it won't happen. I don't see anyone financial benefit.
I haven't seen any new robots doing pick & place with through hole parts. It is hard to imagine such a robot would have enough financial advantage over SMT to make it worthwhile.
The assembly staff who use the components will have to be retrained, and what benefit does the assembly company get?
Through-hole with printed numbers would have to show big benefits to replace coloured rings. AFAIK, SMT has displaced through-hole in the majority of products; robots are cheaper than labour costs humans for mass production.
"Show me the money" - It seems a very tenuous benefit to printing numbers vs lots of cost, especially when the investment has been made already, in a shrinking sector of industry.