The answer is simple: because someone in power said so, and with his thugs buddies pressured the right people to turn it into law - aka "might makes right"
A recent US exemple: civil forfeiture, even of the money you set aside for your own legal representation, is totally ok, even if it actually impedes your right to defend yourself, cf http://www.economist.com/blogs/democracyinamerica/2014/02/ci...
To those who still can't believe civil forfeiture in the US, here is a sweet example in the EU. The constitution explicitely says : "The Union shall not be liable for or assume the commitments of central governments, regional, local or other public authorities, other bodies governed by public law, or public undertakings of any Member State" (article 125 of the Maastricht treaty aka constitution)
Yet the european court of justice, equivalent to the supreme court, found that bailing out Greece etc. by the European Stability Mechanism (purchase of dubious greek debt) was perfectly kosher.
Now people object to the idea of the european central bank doing quantitative easy, for similar reasons - because it's against the basic premises of the ECB, the constitution, etc, but it will be done, regardless of what the law says, if enough pressure is applied by those in power to result in what is in practice disregarding the law.
Basically, you can have a crystal clear constitution saying X is strictly illegal, but unless it's followed in practice, it's as worthless as the freedom of expression that was granted to the citizens of USSR by its own laws.
There used to be a separate judiciary power - even the state was subject to laws. It is no longer the case. This separate power is being swallowed by the state.
Is it profond disrespect of not just the spirit, but the letter, of any constitution? Whatever. "Might makes right"
(Edit: clarified)