Actual historical examples of players switching country, and FAs selecting players of dubious eligibility, and the evolution of the rules to address this, have been discussed elsewhere on this forum so I won't talk casewise.
SDb makes a good point that dual nationality can itself be an imprecise concept (mainly because nationality is), and because the football eligibility rules do not correlate to criteria used for other purposes, there was room for interpretation and thus exploitation. Different countries have their own different passport/citizenship criteria for example, some much stricter than others. So it is natural that an international standardization was imposed (by FIFA) to circumvent the vagaries of different countries' governments. Other sports have done similarly, although there is substantial variation in the criteria across various sports.
So far this is all fine. My point was only to add that the standard rules do not account for genuine cases of dual nationality (e.g. a player with parents of two different nationalities).
In such cases, the rules force a permanent choice to be made for football, and I don't see why this is necessary. It appears to be done only out of an administrative convenience, which is never a good reason for anything.
It is clearly not an effective way of discouraging "Qatar style" cases (players being awarded citizenship later in life only for football purposes) because this happens anyway with the existing rules.
A far more effective rule for dealing with that would be e.g. discounting any "new" nationalities/citizenships acquired as a result of events later in life (post age 21 say).