Node Clustering: Requests are not being distributed

Question

Simultaneous requests are not being handled by different processes. Doesn't seem to be an OS issue as I have tested it on both Windows and Linux.

const express = require('express');
const cluster = require('cluster');
const numCPUs = require('os').cpus().length;

const app = express();
const PORT = 3000;

app.use((req, res, next) => {
    
console.log(`Route ${req.url} handled by ${process.pid}.`);
    next();
});

app.get('/', (req, res) => {
    res.send(`Hello from Node! Request handled by ${process.pid}`);
});

const _delay = (duration) => {
    const startTime = Date.now();
    while (Date.now() - startTime < duration) {
        // does nothing
    }
};

app.get('/timer/:time', (req, res) => {
    _delay(Number(req.params.time));
    res.send(`Time's Up! Request handled by ${process.pid}.`);
});

if (cluster.isPrimary) {
    console.log('Master started...');
    for (let i = 0; i < numCPUs; i++) {
        cluster.fork();
    }
} else {
    app.listen(PORT, () => {
        console.log(`Server started on port ${PORT} with PID ${process.pid} ...`);
    });
}

If I request the blocking route first and then the non-blocking one, they should be handled by different processes, but the entire server is getting blocked.